MATLAB: Interpolation of unequally spaced data

linear interpolation

I have a small set of (x,y) data points which are not evenly spaced. I want to interpolate the data for some analysis work.With very few points I am unable to work out.I cant use interp1 for the data is not evenly spaced.ANY SUGGESTIONS ?

3425.0 12.5 825.0 25 200 37.5 75 50 25 62.5 12.5 75

Best Answer

Your data do not have to be evenly spaced to use interp1.

For example:

x = sort(unique(randi(50,1,10)));
y = randi(10,1,length(x));
xi = linspace(0,max(x),15);
yi = interp1(x,y,xi,'linear');
figure(1)
plot(x,y,'-*b')
hold on
plot(xi,yi,'pr')
hold off
grid
legend('Original','Interpolated')

Related Solutions

MATLAB: How to do cubic interpolation from given sets of data

The interp1 function with the 'pchip' method is the easiest way to do this (for me, anyway).

From the documentation:

'pchip' Shape-preserving piecewise cubic interpolation.

The Code —

x=[0 1 8 12 27];
y=[1 2 3 4 5];
xi = linspace(min(x), max(x));
yi = interp1(x, y, xi, 'pchip');
figure(1)
plot(xi, yi)
hold on
plot(x, y, 'pr', 'MarkerFaceColor','g')
hold off
grid

MATLAB: Does the INTERP1 function in MATLAB handle complex data with the “cubic” method

This enhancement has been incorporated in Release 2006a (R2006a). For previous product releases, read below for any possible workarounds:

The cubic interpolation algorithm is not intended for complex data and hence does not behave well under certain circumstances when the data is complex. As a workaround, use the spline interpolation instead.

Y_spline = interp1(X,Y,Xi,'spline');
plot(X,abs(Y),'b',Xi,abs(Y_spline),'r')

Alternatively, you can split Y into real and imaginary parts, and then interpolate.

Yr = real(Y);
Yi = imag(Y);
Y_cubic = interp1(X,Yr,Xi,'cubic')+i*interp1(X,Yi,Xi,'cubic');
plot(X,abs(Y),'b',Xi,abs(Y_cubic),'r')

Best Answer

Related Solutions

MATLAB: How to do cubic interpolation from given sets of data

MATLAB: Does the INTERP1 function in MATLAB handle complex data with the “cubic” method

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