Technical Solutions

How can I generate a vectorized version of a piecewise-defined function for use in the QUAD or QUADL for functions?

Date Last Modified: Friday, June 26, 2009

Solution ID:		1-1A4J2
Product:		MATLAB
Reported in Release:		R13
Platform:		All Platforms
Operating System:		All OS

 

Subject:

How can I generate a vectorized version of a piecewise-defined function for use in the QUAD or QUADL for functions?

Problem Description:

I have created the following function that represents a piecewise-defined function:
function y = pieces(x)
if (0<=x)&(x<=1)
y = 3*x - 2;
elseif (1<x)&(x<=2)
y = 2 - x;
else
y = 0;
end

However, when I specify this function to the QUAD function:
quad(@pieces,-5,5)
I get the following error:
??? Index exceeds matrix dimensions.

Error in ==> quad.m
On line 67 ==> if ~isfinite(y(7))

Solution: The QUAD function expects the integrating function to input a vector and return a vector of the same size. The given function will accept a vector, but returns a scalar. Update your function with the vectorized version of this piecewise-defined function which is: function y = pieces(x) I1 = (0 <= x) & (x < 1); I2 = (1 <= x) & (x < 2); I3 = ~I1 & ~I2; y = x; % Create y same size as x y(I1) = 3*x(I1) + 2; y(I2) = 2 - x(I2); y(I3) = 0;

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