MATLAB: Saving an interpolated function to an m-file

functionsinterpolationMATLABsave

I have some complicated function that I have interpolated using interp1() so that evaluating it is much faster. I would like the result of this interpolation to be available systemwide by saving it as a function in an .m-file. An example:

xd = -1:0.01:1;
yd = xd.^2;
f = @(x) interp(xd, yd, x);

Is there a way to save the result f to f.m such that I can evaluate f(x) anywhere?

Best Answer

Hi,

To my understanding, you want to save the custom interpolation as function to be available for further evaluation.

For that you can write the code as a MATLAB function.

Here is a sample version for the example code you provided

function res = f(x) 
    xd = -1:0.01:1; 
    yd = xd.^2;  
    res =  interp(xd, yd, x); 
end

Hope this helps.

Related Solutions

MATLAB: M-file function

Your function is calling itself without approaching any convergance or something that will allow it to end. Therefore it will run forever and eventually out of memory (hence the error). Try splitting it up into a script and a function as so:

Script:

 %creating window of plot from -5 to 50 using stepsize 0.25 for t x-axis
 %t should be on the x axis, v should be on the y axis
 k=0; 
for i= -5:.25:50
    k = k+1;
    t(k)=i;
    v(k)=vPieceWise(t(k));
end 
plot(t,v);
 
figure
plot(t,v);
hold on

Function:

%Part A: Mfile function to compute v as a function of t
function v = vPieceWise(t)
 if (t < 0)
        v = 0;
    elseif (0 <= t)&&(8<=16)
        v = -5*t+10*t.^2;
    elseif (8<=16)&&(t<=16)
        v = 624 - 3*t;
    elseif (t<=16)&&(t<=26)
        v = 12*(t-16).^2+36*t;
    elseif (26<t)
        v = 2136*exp(-0.1*(t-26));
 end

MATLAB: Matlab M-File

You should review the documentation on how to write a function, since your above code is not a correctly written function. First, come up with a name for your function, e.g. myFunction. Then create a new file called myFunction.m somewhere on the MATLAB path (e.g. your working directory). Then in that file put your code. E.g.,

function result = myFunction(V)
result = V;  % <-- allocate the result variable, copying all elements
%

% Insert your code here to create the result variable from the V variable
%
return
end

I will give you some hints about correcting your code:

Change this loop:

for i=1:1:6;  % <-- hard coded for exactly 6 elements

to this

for i=1:numel(V)  % <-- allows any size input

The following test has an error in the logic (compare this carefully with the requirement):

if [V(i)<0 | mod(V(i),2)==0 | mod(V(i),4)==0]

The following line has an error on the right hand side calculation (compare this carefully with the requirement):

    V(i)=i*i;

If you don't see what the errors are, step through a small example by hand and compare that to the code result. E.g., at the command line type this:

V=[10,4,7,-8,-3,-12];
myFunction(V)

Best Answer

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