MATLAB: Working around “Index exceeds matrix dimensions”

if statementindexindexingMATLAB

I am looking for peaks in a trace with the following code.

 for i= 1:length(y)
       if y(i) < -0.02 && y(i-1) > -0.02
   c=c+1;  
        n(c,:)=abs(y(i:i+npts-1));   
       end
   end

sometimes i get the error "Index exceeds matrix dimensions" if a peak happens at the end of the trace and there aren't enough points to populate the row in "n"

I would like to either ignore this peak or fill the the missing positions with zeros. Any suggestions on how?

Thanks

Best Answer

In case anyone is wondering I got around the issue with the following

 if(y(i) >0.05 && y(i-1) < 0.05) &&( (length(y)-i >= npts))

if both conditions aren't met then it doesn't do anything.

Related Solutions

MATLAB: Index in position 1 is invalid. Array indices must be positive integers or logical values.

So when I calculate the index, it is 1.7290e+03. Calling "index" in the code throws an error, but copying and pasting "1.729e+03" directly into the argument of the cell array does work.

You calculated index is displayed as 1729 but the value stored in the variable is actually very slightly different from 1729.

>> x = 0;
>> for k = 1:10
  x = x + 0.1;
end
>> x
x =
                         1
>> d = x-1
d =
     -1.11022302462516e-16

As stated on the second page of this Cleve's Corner article from 1996:

"Ten steps of length t are not precisely the same as one step of length 1. MATLAB is careful to arrange that the last element of the vector 0:0.1:1 is exactly equal to 1, but if you form this vector yourself by repeated additions of 0.1, you will miss hitting the final 1 exactly."

You're doing something similar, expecting your calculations to give an exact integer value but instead getting something that just misses hitting that integer value exactly.

Where possible, avoid computing array indices. If you must, compute using only operations on integer values that must give integer values if at all possible or round if not.

MATLAB: Index exceeds matrix dimensions help

There are so many issues. Let's address your error first. Your counter variable n is bigger than the size of your y vector (on this line, Yv=(y(n+1)-(y(n)))/0.0005;). Hence you get the error.

Nevertheless you don't really calculate velocity. You simply initialize v vector with zeros and and trying to calculate only one element (because m is just 1 and you don't have a loop to calculate the other elements).

If you want to carry out your calculations with a loop (Matlab is much more powerful, no loops are needed for your problem though), simply use one loop with a counter variable like below.

your constants here
Theta=0:0.001:(2*pi);
numOfElements = numel(Theta);
y = zeros(1,numOfElements);
v = zeros(1,numOfElements);
for count = 1:numOfElements
    y(count) = something like a*theta(count)*bla*blabla
    v(count) = something else
end

Best Answer

Related Solutions

MATLAB: Index in position 1 is invalid. Array indices must be positive integers or logical values.

MATLAB: Index exceeds matrix dimensions help

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