GradientDecentNeuralNetwork.js

NeuralNetwork.js

class NeuralNetwork {
    constructor(input, goal, iterations){
        this.input = input;
        this.goal = goal;
        this.iterations = iterations;
        this.weight = 0.5;
    }

    predict(){
        let prediction;

        for(let i = 0; i < this.iterations; i++){
            prediction = this.input * this.weight; // try a prediction by multiplying input by weight

            // delta is the derivative of weight verses the error, our goal is to minimise the error (delta^2) as much as posssible
            // delta === ((this.input * this.weight) - this.goal)
            // input and goal are fixed where weight is not, the goal then is the figure out how we can change this.weight to minimise error as much as possible
            const delta = prediction - this.goal; // how far did we miss? the sign of delta tells us if we were too high or too low (positive verses negative)


            // we get the next weight value by multiplying the delta by the input, this gives us negative reversal, stopping and scaling
            const weight_delta = delta * input; // multiply the delta by the input

            this.weight -= weight_delta; // deduct amount missed from the weight

            console.log(
                "Prediction: " + prediction + 
                "\n" + 
                "Error: " + Math.pow(delta, 2) + 
                "\n" + 
                "Missed by: " + delta + 
                "\n" + 
                "Moving weight by: " + weight_delta + 
                "\n" + 
                "New Weight: " + this.weight + 
                "\n\n"
            );
        }

        return prediction;
    }
}

const input = 0.5;
const goal = 0.8;
const iterations = 20;

const neuralNetwork = new NeuralNetwork(input, goal, iterations);

console.log(neuralNetwork.predict())

output.txt

imjacobclark$ node NeuralNetwork.js 
Prediction: 0.25
Missed by: -0.55
Moving weight by: -0.275
New Weight: 0.775


Prediction: 0.3875
Missed by: -0.41250000000000003
Moving weight by: -0.20625000000000002
New Weight: 0.9812500000000001


Prediction: 0.49062500000000003
Missed by: -0.309375
Moving weight by: -0.1546875
New Weight: 1.1359375


Prediction: 0.56796875
Missed by: -0.23203125000000002
Moving weight by: -0.11601562500000001
New Weight: 1.251953125


Prediction: 0.6259765625
Missed by: -0.17402343750000004
Moving weight by: -0.08701171875000002
New Weight: 1.33896484375


Prediction: 0.669482421875
Missed by: -0.1305175781250001
Moving weight by: -0.06525878906250004
New Weight: 1.4042236328125


Prediction: 0.70211181640625
Missed by: -0.09788818359375007
Moving weight by: -0.04894409179687503
New Weight: 1.453167724609375


Prediction: 0.7265838623046875
Missed by: -0.07341613769531252
Moving weight by: -0.03670806884765626
New Weight: 1.4898757934570312


Prediction: 0.7449378967285156
Missed by: -0.05506210327148442
Moving weight by: -0.02753105163574221
New Weight: 1.5174068450927733


Prediction: 0.7587034225463867
Missed by: -0.04129657745361337
Moving weight by: -0.020648288726806685
New Weight: 1.53805513381958


Prediction: 0.76902756690979
Missed by: -0.030972433090210028
Moving weight by: -0.015486216545105014
New Weight: 1.553541350364685


Prediction: 0.7767706751823426
Missed by: -0.023229324817657493
Moving weight by: -0.011614662408828746
New Weight: 1.5651560127735138


Prediction: 0.7825780063867569
Missed by: -0.017421993613243147
Moving weight by: -0.008710996806621574
New Weight: 1.5738670095801353


Prediction: 0.7869335047900676
Missed by: -0.013066495209932416
Moving weight by: -0.006533247604966208
New Weight: 1.5804002571851015


Prediction: 0.7902001285925507
Missed by: -0.009799871407449312
Moving weight by: -0.004899935703724656
New Weight: 1.5853001928888262


Prediction: 0.7926500964444131
Missed by: -0.007349903555586956
Moving weight by: -0.003674951777793478
New Weight: 1.5889751446666196


Prediction: 0.7944875723333098
Missed by: -0.005512427666690245
Moving weight by: -0.0027562138333451225
New Weight: 1.5917313584999646


Prediction: 0.7958656792499823
Missed by: -0.004134320750017739
Moving weight by: -0.0020671603750088696
New Weight: 1.5937985188749735


Prediction: 0.7968992594374867
Missed by: -0.0031007405625133044
Moving weight by: -0.0015503702812566522
New Weight: 1.5953488891562302


Prediction: 0.7976744445781151
Missed by: -0.0023255554218849506
Moving weight by: -0.0011627777109424753
New Weight: 1.5965116668671726


0.7976744445781151