Online polynomial linear curve fitting in Simulink

How to fit curves in Simulink and still generate the code?

I have a model of a sensor in Simulink, that returns vectors "Pos_x" and "Pos_y". Each vector has size of 20x1, whose values change every one step time (1ms).

I am trying to calculate the coeffecients of the 3rd degree Polynomial y(x) = p1*x^3 + p2*x^2 + p3*x + p4 in Simulink, that fits the data.

I did not find any block in simulink that calculates the coeffecients, so I used a simple Matlab function

function [p1, p2, p3, p4] = fcn(x,y)

% f(x) = p1*x^3 + p2*x^2 + p3*x + p4

f = fit(x', y', 'Poly3'); % I have also tried "polyfit"

p1 = f.p1;

p2 = f.p2;

p3 = f.p3;

p4 = f.p4;

end

but I get the error: Function 'fit' not supported for code generation.

1- so back to my qustion, How to fit curves in Simulink and still generate the code?

2- I am also open to any other suggestion

Answer 1

[Jonas]

If you have the DSP Systems Toolbox you can use the Least Squares Polynomial Fit block.

Standard Simulink does not have an alternative as far as I can see. Unless you implement a curve fitting algorithm yourself in a MATLAB Function block. If it is just for testing some stuff the DSP Systems Toolbox seems the alternative.

[Ehab Abdelkarim]

I have found the block but I could not use it, because it accepts only one input, and in my case both X and Y should be Inputs, soI have tried to manipulate the block, so that it accepts 2 inputs but it did not work for me.

[Ehab Abdelkarim]

Thanks for the idea Jonas. finally I could manipulate the Block to adapt to my case.