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MATLAB Matrix dimensional error in numerical integration

  1. Apr 2, 2012 #1
    Hi,
    I tried to numerically integrate an equation in matlab using the trapezium method. Here is the code that I wrote:

    ao = 1;
    X = 0:ao/10:ao;
    Y = 1/sqrt((power(Ho,2)*((O_m*power(X,-1))+(O_r*power(X,-2))+(O_l*power(X,2))))-(k*power(c,2)));
    age = trapz(X,Y);

    where the values for O_m, O_r, O_l and k were obtained using input(). When I executed the above code, I get "Error using / Matrix dimensions must agree."

    Can you tell me what the problem is?

    Sarrvesh
     
  2. jcsd
  3. Apr 2, 2012 #2

    chiro

    User Avatar
    Science Advisor

    Hey sarrfriend.

    MATLABs main data structure is a matrix and it treats pretty much everything in that way. This means that if you do say a * b, a + b and so on, then it assumes that this is going to be a matrix operation and it also assumes that the operations do things in terms of matrix assumptions (AxB a is axb, B is bxc and so on). This is why you get the error.

    What you need to do if you want to do a component by component arithmetic operation is put a "." before the operation. For example lets say we have a vector A [0,1,2,3,4,5] and another vector B [0,2,4,6,8,10]. Then if we write C = A .* B we get [0,2,8,18,32,50]. If you want to do exponentiation just use .^ operator instead of power which will do a component wise exponentiation.

    If you want to know more create a few row vectors of the same size and try .* ./ and .^ and see what you get in the output.
     
  4. Apr 2, 2012 #3
    Hi Chiro,
    Thanks the info. It worked.

    Sarrfriend
     
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