MATLAB: Simple solution to manuplate matrix

matrix manipulation

consider i have matrix A=[1 2 3 4 5 6 7 8 9 ]; B=[9 8 7]; i want to add them in such a way that C= A+B = [1 2 3 4 5 6 ,9 8 7]; i used the for loop but it takes too much processing time wonder if there is qa simple solution to this

as=size(A); bs=size(B); for r= 1: as(2)-bs(2); cs(1,r)=A(1,r); end C=[cs,B];

Best Answer

Hi saif,

From your code example, it appears that you wish only to replace the last three elements of A with the three elements of B. Is that correct? If that is the case, then you could do something like:

C = [A(1:length(A)-length(B)) B];

So in the above, the length(A) returns the number of elements in vector A and length(B) returns the number of elements in vector B. We then copy all of A except for those elements that are to be replaced by B, A(1:length(A)-length(B)) and then use the square brackets to concatenate that result with B.

There are two problems with the above code - it does not handle the case where the length of B is greater than the length of A, and it assumes that both A and B are vectors and not matrices.

Hope that this helps!

Geoff

Related Solutions

MATLAB: How to write a function that returns the element that is the center of a vector or matrix

Hi Kimberly,

Your function signature could look something like this:

function [ctr] = find_centre (x)

<code to be filled in by you!>

end

where x is your input (from your examples 1233 or [123;458;112]) and ctr is the found centre of the x (again from your examples, [2 3] or [2;5;1]).

I'm guessing that if your input is a matrix then the output should be the centre of each row?

Since you say that your input can be a vector or a matrix (a string of characters can be a vector so whether your input is a row of characters, numbers, cells, or whatever, the logic should be the same) then you probably want to handle the inputs separately by checking to see if x is a vector or is a matrix using the isvector and ismatrix functions respectively. (Note that a vector can be a matrix but not the other way around, so you will want to start with the vector check.)

If the input is a vector, then check its size/length using either of numel (number of elements) or length. The centre of your vector then will be dependent upon whether the size is even or odd (as you have shown in your examples) and you can then extract it from x and set it in ctr via the ctr = x(cstart:cstop); where cstart and cstop are the centre start and stop indices within the vector. From your example of 1223, then cstart=2 and cstop=3. If just 123, then cstart=2 and cstop=2 as well.

If the input is a matrix then you can get the number of rows and columns and do something similar to the above.

Geoff

MATLAB: Combining 2 Arrays(of equal or different dimensions)

First Exercise: If we create C2 that is an array of zeros which has double the length of A2 and B2 combine. We can space A2 and B2 every 2 element apart and then remove the 0 inside the array.

% creating the C2 array of zeros which has double the length of A2 and B2 combine. 
lenA2 = length(A2)*2;
lenB2 = length(B2)*2;
C2 = zeros(1,(lenA2 + lenB2));
% place A2 and B2 in every 2nd element after the starting point
C2(1:2:lenA2) = A2;
C2(2:2:lenB2) = B2;
% removes 0 in the array
C2(C2 == 0) = [];

Best Answer

Related Solutions

MATLAB: How to write a function that returns the element that is the center of a vector or matrix

MATLAB: Combining 2 Arrays(of equal or different dimensions)

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