# Matlab Numerical Integration - Syntax/Style Query

by pete j
Tags: integration, matlab
 P: 1 Hi, Pretext: I have no formal background in matlab or maths in general, so apologies if any of the following doesn't make sense. I am also new to this forum, so apologies if this post is incorrect in any way. [n.b. I also posted this thread on mathhelpforum.com] Context: Ok, so I wanted to find the response value for various parameter values, using the following equation: [If you can't see the image, it is an integration with infinite bounds over an equation consisting of a Gaussian probability density function multiplied by the the square of a Gaussian cumulative density function plus one minus the square of another Gaussian cumulative density function] I wasn't sure whether it was possible to do this using the matlab symbolic toolkit (syms), so I thought I'd take a crack at it using numerical integration, using the quad command. After much effort and confusion, I ended up with the following code. mu=0; sigma=1; s=0; alpha=0.4; mu=sprintf('%f', mu); sigma=sprintf('%f', sigma); s=sprintf('%f', s); alpha=sprintf('%f', alpha); f=strcat('normpdf(x+',s,',',mu,',sqrt(2)*',sigma,').*(normcdf(x,',mu,',sqrt(2)*',alpha,'*',sigma,').^2 + (1 - normcdf(x,',mu,',sqrt(2)*',alpha,'*',sigma,')).^2)'); quad(f,-1000,1000) This code *DOES* appear to work (i.e. yields the expected answers). But it strikes me as being more than a little crude. My questions therefore are as follows: From a mathematical point of view, was using numerical integration with suitably wide bounds the right way to go about this problem? From a programming point of view, is there a more elegant way to execute the above numerical integration? (i.e. a better approach than wrapping everything up as one big string which is then passed to the quad function) Many thanks for your time, Best, pete