How to implement Hermite spline in Simulink

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MARCO LORENZI 2021-9-22

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https://ww2.mathworks.cn/matlabcentral/answers/1458289-how-to-implement-hermite-spline-in-simulink

编辑： MARCO LORENZI 2021-9-24

Good morning everyone.

Can i ask if it there is a way to implement the Hermite spline (pchip) or Bezier curves in simulink?

In particular, i am using a look-up table to interpolate a curve between some point, but the cubic and akima splines don't do a good job. I was thinking about using a linear interpolating method and then smoothen up the curves, but i can't find any blockset.

Thank you very much in advance.

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Answer 1

Bjorn Gustavsson 2021-9-22

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There is a way to make blocks that wrap a matlab-function (matlab-functions-simulink_5), shouldn't that solve this task?

HTH

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MARCO LORENZI 2021-9-24

编辑：MARCO LORENZI 2021-9-24

Cattura.PNG

Hi, i am sorry to bother again but i have 1 last question.

So in the picture i attached i wanted to show what i wanted to do (substitute the lookup tables). In the two block is going to enter a number between 0 and 90 deg.

The output of the upper block says that if the input is <15 the output must be 1 and if >15 the output must be 0. The transition from 1 to 0 is made between 15 and 30deg.

The output of the lower block says that if the input is <15 the output must be 0 and if >15 the output must be 1 The transition from 1 to 0 is made between 15 and 30deg.

I plugged this code for the upper block

function output = low_angles_Hermite_approximation(phase)

x = length(phase);

y = [0 0 0 0 0 0 0 1 1];

xq = [0 2.5 5 7.5 10 13 15 30 90];

output = pchip(x,y,xq);

I plugged this code for the lower block

function output = low_angles_Hermite_approximation(phase)

x = length(phase);

y = [1 1 1 1 1 1 1 0 0];

xq = [0 2.5 5 7.5 10 13 15 30 90];

output = pchip(x,y,xq);

Matlab returns the error "The first two inputs must have at least two elements"

MARCO LORENZI 2021-9-24

i don't think it is hard but i do not know how to do it. Basically, based on the input, that goes from 0 to 90, the first block does this:

The second one this:

And the output is y.

Bjorn Gustavsson 2021-9-24

在 MATLAB Online 中打开

To me it seems as you swapped the x and xq in the function. It ought to be:

function output = low_angles_Hermite_approximation(phase)
xq = phase;
y = [0 0 0 0 0 0 0 1 1];
x = [0 2.5 5 7.5 10 13 15 30 90];
output = pchip(x,y,xq);

When you program and run into errors like these read the help and documentation carefully - and calmly, far to often it is easy to rush that part. Also be prepared to use the debug-facilities of matlab, I typically turn on debug-stop after an error:

>> dbstop if error

Then you get a command-line prompt at the line where the error occurred with command-line access to all variables in the function and it is possible to step up in the function call-stack.

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