What is wrong with this Matlab code? Simple While Loop

Question

Totally new at MatLab and I need it to answer this homework question for my class. I'm trying to see when this equation (mu) will equal a certain value (sae30mu) while decreasing x so that I can find the correct value for x. However, when it prints x, I get a negative number. I cannot tell why this code won't work, as it appears (to me) that it should just spit out the answer.

  x = 1.0;
   mu = ((sae10mu)^x)*((sae50mu)^(1-x));

   while (mu ~= sae30mu & x >= 0)
       x = x - 0.01;
       mu = ((sae10mu)^x)*((sae50mu)^(1-x));
   end

   x

David · Accepted Answer · 2014-09-11 03:25:10Z

4

There are two problems here.

Firstly, you aren't getting the right answer because mu will never equal sae10mu, so mu~=sae10mu will always be true. Limits of numerical precision mean that you can't do floating point comparison like this. Instead, you need to define some tolerance, tol, and do a comparison like abs(mu-sae10mu)>tol. Then, once mu is within tol of sae10mu, the condition will be true.

Secondly, the x>=0 will be true until x is less than 0. The first value you will get to is the largest value of x less than 0, which is -0.01. To stop at x=0, do x>0.

Your while loop should look like this: while(abs(mu-sae10mu)>tol & x>0).

answered Sep 11, 2014 at 3:25

David

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1 Comment

Dan Over a year ago

Technically it should also use && instead of just & as well

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