Generating a function using an array

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Brian Kettering 2020-8-26

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https://ww2.mathworks.cn/matlabcentral/answers/584813-generating-a-function-using-an-array

编辑： esat gulhan 2020-8-26

If I have an array of data. Is there a way to generate a function from the data contained in the array? That if I evaluated the function, it would generate the data equivelent to the array. The generated function will be used to find the local min and max (critical points) of the function.

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Answer 1

esat gulhan 2020-8-26

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maybe like this. if you send data it can be easier to choose the way of function. I used sin data and choose pchip.

x=[ 0  0.3142  0.6283  0.9425  1.2566  1.5708   1.8850  2.1991  2.5133  2.8274 3.1416  3.4558   3.7699    4.0841]    
y=[ 0  0.3090  0.5878  0.8090  0.9511  1.0000   0.9511  0.8090  0.5878  0.3090 0.0000  -0.3090 -0.5878   -0.8090]  
t=pchip(x,y) %Piecewise Cubic Hermite Interpolating Polynomial function of x y
ppval(t,2) %the value of function at 2
ppval(t,0) %the value of function at 0
plot(x,ppval(t,x))
findpeaks(ppval(t,x)) %local maksimum points

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Brian Kettering 2020-8-26

scope_0.csv

Here' the .csv file:

Brian Kettering 2020-8-26

Thanks for helping, but I keep getting the following error

Error using chckxy (line 30)

The X vector should have real elements.

Error in pchip (line 58)

[x,y,sizey] = chckxy(x,y);

Error in Untitled2 (line 11)

t=pchip(x,y) %Piecewise Cubic Hermite Interpolating Polynomial function of x y

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Answer 2

esat gulhan 2020-8-26

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/584813-generating-a-function-using-an-array#answer_485363

编辑：esat gulhan 2020-8-26

在 MATLAB Online 中打开

Hi

can you try this

clear all;clc;
x=[ 0  0.3142  0.6283  0.9425  1.2566  1.5708   1.8850  2.1991  2.5133  2.8274 3.141  3.4558  3.76  4.08]    
y=[ 0  0.3090  0.5878  0.8090  0.9511  1   0.9511  0.809  0.5878  0.3090 0.0  -0.309 -0.58  -0.8]  
t=pchip(x,y) %Piecewise Cubic Hermite Interpolating Polynomial function of x y
ppval(t,2) %the value of function at 2
ppval(t,0) %the value of function at 0
plot(x,ppval(t,x))
findpeaks(ppval(t,x)) %local maksimum points