how to realize look up function in m script

hello, i have x axle table and y axle table, when i set value within the range of x, how to get the output from y, may be some interpolation and curve smoothing should used. i hope it works in m script.

[Mathieu NOE]

hello

sure , you can use interpolation (with interp1 ) or you can also fit a polynomial with polyfit

1-D data interpolation (table lookup) - MATLAB interp1 - MathWorks France

Ajuster des courbes polynomiales - MATLAB polyfit - MathWorks France

[wenchao zhang]

hi,Mathieu, if i just want use simple smooting method,not consider polynominal,how to do

[Star Strider]

The interp1 function has several method options, depending on what you want to do.

For example:

xi = 90;

yi = interp1(x, y, xi, 'linear')

yi = interp1(x, y, xi, 'pchip')

To find a value of ‘x’ that corresponds to a specific value of ‘y’, simply reverse the arguments:

yi = 90;

xi = interp1(y, x, yi, 'linear')

xi = interp1(y, x, yi, 'pchip')

Fortunately, ‘y’ appears to be a monotonically increasing function of ‘x’. If that were not the situation, it would be necessary to determine the approximate indices of the ‘x’ values where ‘y’ crossed a specific value, and then interpolate in each region in a for loop.

.

[Mathieu NOE]

@wenchao zhang

if you can , share yur data and we can show you some options (if you are unsure how to proceed)

[wenchao zhang]

ok, i wiil share data later.

[wenchao zhang]

extreploation need consider, if input x is out of range

[Walter Roberson]

xi = interp1(y, x, yi, 'linear', 'extrap')

[wenchao zhang]

yes,you are right.

Answer 1

[wenchao zhang]

use interp1 seems ok,

x = 0:pi/4:2*pi;
v = sin(x);
xq = 0:pi/16:2*pi;
figure
vq2 = interp1(x,v,xq,'spline');
plot(x,v,'o',xq,vq2,':.');
xlim([0 2*pi]);
title('Spline Interpolation');