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Fix pow recursive and gradient functions #42

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Fix pow recursive and gradient functions #42

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18 changes: 10 additions & 8 deletions src/tensor.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -717,7 +717,7 @@ export class Pow {
*/
forward(a: Tensor, n: number): Tensor {
// Build cache to use in backward step:
this.cache = a;
this.cache = [a, n];

// Call recursive function:
const z = new Tensor(
Expand All @@ -737,12 +737,12 @@ export class Pow {

backward(dz: Tensor, z: Tensor) {
// Get data from cache:
const a = this.cache;
const [a, n] = this.cache;

// Find gradients relative to "a", and pass them downstream:
if (requiresGrad(a)) {
// d/da(e^a) = e^a, apply the chain rule to the derivative of e^a:
const da = new Tensor(_mul(2, _mul(a.data, dz.data)));
// d/da(a^n) = na^(n-1), apply the chain rule to the derivative of a^n:
const da = new Tensor(_mul(n, _mul(_pow(a.data, n-1), dz.data)));
a.backward(da, z);
}
}
Expand Down Expand Up @@ -1725,11 +1725,13 @@ function _matmul(a: Array<any>, b: Array<any>, kernel: any): Array<any> {

function _pow(a: Array<any> | number, n: number): Array<any> | number {
// If a is a number, exponentiate it. If not, exponentiate all of its elements:
let z = a;
for (let i = 0; i < n - 1; i++) {
z = _mul(z, a);
if (typeof a === "number") {
return a ** n;
} else if (a instanceof Array) {
return a.map((element: Array<any>) => _pow(element, n))
} else {
throw new TypeError("the input data is not a number.");
}
return z;
}

function _sqrt(a: Array<any> | number): Array<any> | number {
Expand Down