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# 0. Basic LLM Concepts
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## Pretraining
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Pretraining ni hatua ya msingi katika kuendeleza mfano mkubwa wa lugha (LLM) ambapo mfano unakabiliwa na kiasi kikubwa na tofauti za data za maandiko. Wakati wa hatua hii, **LLM inajifunza miundo, mifumo, na nuances za lugha**, ikiwa ni pamoja na sarufi, msamiati, sintaksia, na uhusiano wa muktadha. Kwa kuchakata data hii kubwa, mfano unapata uelewa mpana wa lugha na maarifa ya jumla ya ulimwengu. Msingi huu wa kina unamwezesha LLM kuunda maandiko yanayofaa na yanayohusiana na muktadha. Baadaye, mfano huu ulioandaliwa unaweza kupitia marekebisho, ambapo unafundishwa zaidi kwenye seti maalum za data ili kubadilisha uwezo wake kwa kazi au maeneo maalum, kuboresha utendaji wake na umuhimu katika matumizi yaliyokusudiwa.
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## Main LLM components
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Kawaida LLM inajulikana kwa usanidi unaotumika kuifundisha. Hizi ndizo sehemu za kawaida wakati wa kufundisha LLM:
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- **Parameters**: Parameters ni **uzito na upendeleo unaoweza kujifunzwa** katika mtandao wa neva. Hizi ni nambari ambazo mchakato wa mafunzo unarekebisha ili kupunguza kazi ya hasara na kuboresha utendaji wa mfano kwenye kazi. LLM mara nyingi hutumia mamilioni ya parameters.
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- **Context Length**: Hii ni urefu wa juu wa kila sentensi inayotumika kuandaa LLM.
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- **Embedding Dimension**: Ukubwa wa vector inayotumika kuwakilisha kila token au neno. LLM mara nyingi hutumia bilioni za dimensions.
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- **Hidden Dimension**: Ukubwa wa tabaka zilizofichwa katika mtandao wa neva.
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- **Number of Layers (Depth)**: Idadi ya tabaka ambazo mfano unazo. LLM mara nyingi hutumia tabaka kumi.
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- **Number of Attention Heads**: Katika mifano ya transformer, hii ni idadi ya mitambo tofauti ya umakini inayotumika katika kila tabaka. LLM mara nyingi hutumia vichwa vingi.
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- **Dropout**: Dropout ni kama asilimia ya data inayondolewa (uwezekano unakuwa 0) wakati wa mafunzo inayotumika **kuzuia overfitting.** LLM mara nyingi hutumia kati ya 0-20%.
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Configuration of the GPT-2 model:
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```json
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GPT_CONFIG_124M = {
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"vocab_size": 50257, // Vocabulary size of the BPE tokenizer
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"context_length": 1024, // Context length
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"emb_dim": 768, // Embedding dimension
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"n_heads": 12, // Number of attention heads
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"n_layers": 12, // Number of layers
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"drop_rate": 0.1, // Dropout rate: 10%
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"qkv_bias": False // Query-Key-Value bias
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}
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```
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## Tensors katika PyTorch
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Katika PyTorch, **tensor** ni muundo wa data wa msingi unaotumikia kama array ya multidimensional, ukijumlisha dhana kama scalars, vectors, na matrices kwa vipimo vya juu zaidi. Tensors ndio njia kuu ambayo data inawakilishwa na kushughulikiwa katika PyTorch, hasa katika muktadha wa deep learning na neural networks.
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### Dhana ya Kihesabu ya Tensors
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- **Scalars**: Tensors za kiwango cha 0, zinazoakisi nambari moja (dimensional sifuri). Kama: 5
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- **Vectors**: Tensors za kiwango cha 1, zinazoakisi array ya nambari za dimensional moja. Kama: \[5,1]
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- **Matrices**: Tensors za kiwango cha 2, zinazoakisi arrays za dimensional mbili zikiwa na safu na nguzo. Kama: \[\[1,3], \[5,2]]
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- **Tensors za Kiwango cha Juu**: Tensors za kiwango cha 3 au zaidi, zinazoakisi data katika vipimo vya juu (mfano, tensors za 3D kwa picha za rangi).
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### Tensors kama Vifungashio vya Data
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Kutoka kwa mtazamo wa hesabu, tensors hufanya kazi kama vifungashio vya data za multidimensional, ambapo kila kipimo kinaweza kuwakilisha vipengele tofauti au nyanja za data. Hii inafanya tensors kuwa na uwezo mkubwa wa kushughulikia seti za data ngumu katika kazi za machine learning.
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### Tensors za PyTorch vs. NumPy Arrays
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Ingawa tensors za PyTorch zinafanana na arrays za NumPy katika uwezo wao wa kuhifadhi na kushughulikia data za nambari, zinatoa kazi za ziada muhimu kwa ajili ya deep learning:
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- **Automatic Differentiation**: Tensors za PyTorch zinasaidia hesabu ya moja kwa moja ya gradients (autograd), ambayo inarahisisha mchakato wa kuhesabu derivatives zinazohitajika kwa ajili ya mafunzo ya neural networks.
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- **GPU Acceleration**: Tensors katika PyTorch zinaweza kuhamishwa na kuhesabiwa kwenye GPUs, ikiongeza kasi ya hesabu kubwa.
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### Kuunda Tensors katika PyTorch
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Unaweza kuunda tensors kwa kutumia kazi ya `torch.tensor`:
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```python
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pythonCopy codeimport torch
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# Scalar (0D tensor)
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tensor0d = torch.tensor(1)
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# Vector (1D tensor)
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tensor1d = torch.tensor([1, 2, 3])
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# Matrix (2D tensor)
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tensor2d = torch.tensor([[1, 2],
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[3, 4]])
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# 3D Tensor
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tensor3d = torch.tensor([[[1, 2], [3, 4]],
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[[5, 6], [7, 8]]])
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```
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### Aina za Data za Tensor
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PyTorch tensors zinaweza kuhifadhi data za aina mbalimbali, kama vile nambari nzima na nambari za kuogelea.
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Unaweza kuangalia aina ya data ya tensor kwa kutumia sifa ya `.dtype`:
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```python
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tensor1d = torch.tensor([1, 2, 3])
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print(tensor1d.dtype) # Output: torch.int64
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```
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- Tensors zilizoundwa kutoka kwa nambari za Python ni za aina `torch.int64`.
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- Tensors zilizoundwa kutoka kwa floats za Python ni za aina `torch.float32`.
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Ili kubadilisha aina ya data ya tensor, tumia njia ya `.to()`:
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```python
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float_tensor = tensor1d.to(torch.float32)
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print(float_tensor.dtype) # Output: torch.float32
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```
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### Common Tensor Operations
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PyTorch inatoa aina mbalimbali za operesheni za kushughulikia tensors:
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- **Accessing Shape**: Tumia `.shape` kupata vipimo vya tensor.
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```python
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print(tensor2d.shape) # Output: torch.Size([2, 2])
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```
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- **Reshaping Tensors**: Tumia `.reshape()` au `.view()` kubadilisha umbo.
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```python
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reshaped = tensor2d.reshape(4, 1)
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```
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- **Transposing Tensors**: Tumia `.T` kubadilisha tensor ya 2D.
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```python
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transposed = tensor2d.T
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```
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- **Matrix Multiplication**: Tumia `.matmul()` au opereta `@`.
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```python
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result = tensor2d @ tensor2d.T
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```
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### Importance in Deep Learning
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Tensors ni muhimu katika PyTorch kwa ajili ya kujenga na kufundisha mitandao ya neva:
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- Wanahifadhi data za ingizo, uzito, na bias.
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- Wanarahisisha operesheni zinazohitajika kwa ajili ya kupita mbele na nyuma katika algorithimu za mafunzo.
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- Pamoja na autograd, tensors zinawezesha hesabu ya moja kwa moja ya gradients, ikirahisisha mchakato wa optimization.
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## Automatic Differentiation
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Automatic differentiation (AD) ni mbinu ya kompyuta inayotumika **kuthibitisha derivatives (gradients)** za kazi kwa ufanisi na kwa usahihi. Katika muktadha wa mitandao ya neva, AD inawezesha hesabu ya gradients zinazohitajika kwa **algorithimu za optimization kama gradient descent**. PyTorch inatoa injini ya utofautishaji wa moja kwa moja inayoitwa **autograd** ambayo inarahisisha mchakato huu.
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### Mathematical Explanation of Automatic Differentiation
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**1. The Chain Rule**
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Katika msingi wa utofautishaji wa moja kwa moja ni **chain rule** kutoka kwa calculus. Chain rule inasema kwamba ikiwa una muundo wa kazi, derivative ya kazi iliyounganishwa ni bidhaa ya derivatives za kazi zilizounganishwa.
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Kihesabu, ikiwa `y=f(u)` na `u=g(x)`, basi derivative ya `y` kwa heshima na `x` ni:
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<figure><img src="../../images/image (1) (1) (1) (1) (1).png" alt=""><figcaption></figcaption></figure>
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**2. Computational Graph**
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Katika AD, hesabu zinawakilishwa kama voz katika **computational graph**, ambapo kila voz inahusiana na operesheni au variable. Kwa kupita katika graph hii, tunaweza kuhesabu derivatives kwa ufanisi.
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3. Example
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Hebu tuchukue kazi rahisi:
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<figure><img src="../../images/image (1) (1) (1) (1) (1) (1).png" alt=""><figcaption></figcaption></figure>
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Ambapo:
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- `σ(z)` ni kazi ya sigmoid.
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- `y=1.0` ni lebo ya lengo.
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- `L` ni hasara.
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Tunataka kuhesabu gradient ya hasara `L` kwa heshima na uzito `w` na bias `b`.
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**4. Computing Gradients Manually**
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<figure><img src="../../images/image (2) (1) (1).png" alt=""><figcaption></figcaption></figure>
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**5. Numerical Calculation**
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<figure><img src="../../images/image (3) (1) (1).png" alt=""><figcaption></figcaption></figure>
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### Implementing Automatic Differentiation in PyTorch
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Sasa, hebu tuone jinsi PyTorch inavyofanya mchakato huu kuwa wa moja kwa moja.
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```python
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pythonCopy codeimport torch
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import torch.nn.functional as F
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# Define input and target
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x = torch.tensor([1.1])
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y = torch.tensor([1.0])
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# Initialize weights with requires_grad=True to track computations
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w = torch.tensor([2.2], requires_grad=True)
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b = torch.tensor([0.0], requires_grad=True)
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# Forward pass
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z = x * w + b
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a = torch.sigmoid(z)
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loss = F.binary_cross_entropy(a, y)
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# Backward pass
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loss.backward()
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# Gradients
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print("Gradient w.r.t w:", w.grad)
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print("Gradient w.r.t b:", b.grad)
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```
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```css
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cssCopy codeGradient w.r.t w: tensor([-0.0898])
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Gradient w.r.t b: tensor([-0.0817])
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```
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## Backpropagation katika Mitandao Mikubwa ya Neural
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### **1. Kupanua kwa Mitandao ya Tabaka Mengi**
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Katika mitandao mikubwa ya neural yenye tabaka nyingi, mchakato wa kuhesabu gradients unakuwa mgumu zaidi kutokana na kuongezeka kwa idadi ya vigezo na operesheni. Hata hivyo, kanuni za msingi zinabaki kuwa sawa:
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- **Forward Pass:** Hesabu matokeo ya mtandao kwa kupitisha ingizo kupitia kila tabaka.
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- **Compute Loss:** Kadiria kazi ya hasara kwa kutumia matokeo ya mtandao na lebo za lengo.
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- **Backward Pass (Backpropagation):** Hesabu gradients za hasara kuhusiana na kila parameter katika mtandao kwa kutumia sheria ya mnyororo kwa kurudi kutoka tabaka la matokeo hadi tabaka la ingizo.
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### **2. Algorithm ya Backpropagation**
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- **Hatua ya 1:** Anzisha vigezo vya mtandao (uzito na bias).
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- **Hatua ya 2:** Kwa kila mfano wa mafunzo, fanya forward pass ili kuhesabu matokeo.
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- **Hatua ya 3:** Hesabu hasara.
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- **Hatua ya 4:** Hesabu gradients za hasara kuhusiana na kila parameter kwa kutumia sheria ya mnyororo.
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- **Hatua ya 5:** Sasisha vigezo kwa kutumia algorithm ya uboreshaji (mfano, gradient descent).
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### **3. Uwiano wa Kihesabu**
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Fikiria mtandao rahisi wa neural wenye tabaka moja lililo fichwa:
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<figure><img src="../../images/image (5) (1).png" alt=""><figcaption></figcaption></figure>
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### **4. Utekelezaji wa PyTorch**
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PyTorch inarahisisha mchakato huu kwa injini yake ya autograd.
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```python
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import torch
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import torch.nn as nn
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import torch.optim as optim
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# Define a simple neural network
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class SimpleNet(nn.Module):
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def __init__(self):
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super(SimpleNet, self).__init__()
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self.fc1 = nn.Linear(10, 5) # Input layer to hidden layer
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self.relu = nn.ReLU()
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self.fc2 = nn.Linear(5, 1) # Hidden layer to output layer
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self.sigmoid = nn.Sigmoid()
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def forward(self, x):
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h = self.relu(self.fc1(x))
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y_hat = self.sigmoid(self.fc2(h))
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return y_hat
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# Instantiate the network
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net = SimpleNet()
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# Define loss function and optimizer
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criterion = nn.BCELoss()
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optimizer = optim.SGD(net.parameters(), lr=0.01)
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# Sample data
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inputs = torch.randn(1, 10)
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labels = torch.tensor([1.0])
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# Training loop
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optimizer.zero_grad() # Clear gradients
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outputs = net(inputs) # Forward pass
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loss = criterion(outputs, labels) # Compute loss
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loss.backward() # Backward pass (compute gradients)
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optimizer.step() # Update parameters
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# Accessing gradients
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for name, param in net.named_parameters():
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if param.requires_grad:
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print(f"Gradient of {name}: {param.grad}")
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```
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Katika msimbo huu:
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- **Forward Pass:** Inahesabu matokeo ya mtandao.
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- **Backward Pass:** `loss.backward()` inahesabu gradients za hasara kuhusiana na vigezo vyote.
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- **Parameter Update:** `optimizer.step()` inasasisha vigezo kulingana na gradients zilizohesabiwa.
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### **5. Kuelewa Backward Pass**
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Wakati wa backward pass:
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- PyTorch inatembea kwenye grafu ya hesabu kwa mpangilio wa kinyume.
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- Kila operesheni, inatumia sheria ya mnyororo kuhesabu gradients.
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- Gradients zinakusanywa katika sifa ya `.grad` ya kila tensor ya parameter.
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### **6. Faida za Tofauti Otomatiki**
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- **Ufanisi:** Inakwepa hesabu zisizo za lazima kwa kutumia matokeo ya kati.
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- **Usahihi:** Inatoa derivatives sahihi hadi usahihi wa mashine.
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- **Urahisi wa Matumizi:** Inondoa hesabu ya mikono ya derivatives.
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