summation in matlab help

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mutah il 14 Set 2013

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this is my code to plot summation of 10 normpdf but when i plot figure the plot not like normpdf what the reason ??? plz answer me

w=[0.1139;0.0087;0.6147;0.0437 ; 0.1752;0.0115          ;0.0017;0.0198;0.0034;0.0074   ];
     sigma=[0.0398;0.4716;0.4448;0.2984;0.1466;0.2828;1.3330;0.3010;0.0415;0.3592];
      mu=[0.0074 ;4.9530;0.9306;2.8815;0.5280;4.0052;6.9460;2.4941;0.2566;3.4896];
        x=0:20:80;
        sum=0;
       for i=1:10
       y=w(i)*normpdf(x, mu(i), sigma(i)); 
        sum=sum+y;
      end
       plot(x,sum);
       grid on

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Azzi Abdelmalek il 15 Set 2013

Ok, but that's what your code is doing. If the result is not what you are expecting, then tell us what is the wanted result

Walter Roberson il 15 Set 2013

If I understand correctly, you are expecting that normpdf() will return a vector, since you pass in a vector for x.

I do not have that toolbox, so I cannot experiment to be sure, but it does look to me as if it should be returning a vector.

You should put a breakpoint in on the line after you calculate y, run the program, and examine y to see what result you get.

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Answer 1

Image Analyst il 14 Set 2013

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First of all, DON'T use sum as the name of your variable because you'll no longer have access to the built-in function by that name. Call it "theSum" or something else.

Secondly, all you're doing is adding up a bunch of numbers to get a single number out, then you plot it (or try to). What do you expect to see? sum is not an array and does not have different values for different i - it's just a single number, not an array.

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Azzi Abdelmalek il 14 Set 2013

sum has the same length then x

Image Analyst il 14 Set 2013

I think that either y or theSum might want to take an index: y(i) or theSum(i). Or he could just calculate theSum after the loop if he indexes y: theSum = sum(y). Unfortunately I don't have the normpdf() function so I can't really fix the code, plus lack of comments make it unclear what he wants to do.

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