Math.Net数字 - 拟合窦功能

Question

I'm new here and I hope that perhaps the experts outthere can help me: I want to fit the sinus function f(x) = a *sin(b* (x+c))+d via the library "math.net numerics" in C#.

At the beginning I tried the following example code:

// data points: we compute y perfectly but then add strong random noise to it
var rnd = new Random(1);
var omega = 1.0d
var xdata = new double[] { -1, 0, 0.1, 0.2, 0.3, 0.4, 0.65, 1.0, 1.2, 2.1, 4.5, 5.0, 6.0 };
var ydata = xdata.Select(x => 5 + 2 * Math.Sin(omega*x + 0.2) + 2*(rnd.NextDouble()-0.5)).ToArray();

// build matrices
var X = DenseMatrix.OfColumns(new[] {
new DenseVector(1),
new DenseVector(xdata.Select(t => Math.Sin(omega*t)).ToArray()),
new DenseVector(xdata.Select(t => Math.Cos(omega*t)).ToArray())});
var y = new DenseVector(ydata);

// solve
var p = X.QR().Solve(y);
var a = p[0];
var b = SpecialFunctions.Hypotenuse(p[1], p[2]);
var c = Math.Atan2(p[2], p[1]); 

But the result was, that the program returned the following error:

"Matrix dimensions must agree: 1x3".

Could you give me a hint what I can do to solve the problem ?

Answer 1

You are adding 3 columns to the matrix (X) that have different lengths.

The first vector has length 1, while the second and third vectors have lengths of xdata.Length .

If you intend for the first vector to have the length of xdata.Length but to be filled with 1s then do the following:

var X = DenseMatrix.OfColumns(new[]
{
    new DenseVector(Enumerable.Repeat(1d , xdata.Length).ToArray()),
    new DenseVector(xdata.Select(t => Math.Sin(omega*t)).ToArray()),
    new DenseVector(xdata.Select(t => Math.Cos(omega*t)).ToArray())
});