function - input and output matrix

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Mina
Mina on 21 Jun 2021
Answered: Steven Lord on 22 Jun 2021
I need to write a function that takes a matrix of any size, double all the elements that are positive and adds 10 to all the elements that are zero or negative. I can't use loops, only filters.
the input matrix is xin[n,m] sent by the script and the out variable is xout [n,m]
This is my code:
function xout = matrixfx(xin)
%matrixfx takes a matrix of any size, doubles all the elements that are positive and adds 10 to all
%the elements that are zero or negative.
[n,m] = size(xin);
xout = zeros(n,m);
mask = xin > 0;
xout(mask) = xin(mask) * 2;
xout(~mask) = xin(~mask) + 10;
end
  4 Comments
Steven Lord
Steven Lord on 21 Jun 2021
Okay, can you show us that script? I have a suspicion about what's causing the error but I'd need to see that script to confirm or refute that suspicion.
Mina
Mina on 21 Jun 2021
In the script, the function is used to manipulate the test data and then the elements of the matrix are added up.
x = load ('matrixA.mat');
y = matrixfx(x);
[rows,cols] = size(y);
total = 0;
for i = 1:rows
for j = 1:cols
total = total + y(i,j);
end
end

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Answers (2)

Steven Lord
Steven Lord on 22 Jun 2021
My suspicion was correct. When you call load with an output argument, that output argument is a struct array with each variable in the MAT-file you load stored as a field of that struct. You just need to pull the data out of the struct.
mydata = load('census.mat')
mydata = struct with fields:
cdate: [21×1 double] pop: [21×1 double]
If I wanted to work with the date and population data from census.mat, I would need to use mydata.cdate and mydata.pop rather than mydata (the whole struct array), cdate (which doesn't exist; the data is in the field of mydata), or pop (which also doesn't exist.)
[p, s, mu] = polyfit(mydata.cdate, mydata.pop, 2); % Work with cdate and pop from census.mat

Jan
Jan on 21 Jun 2021
Edited: Jan on 21 Jun 2021
Your code is fine. The only problem is, that you call it with a struct. Unfortunately you show us the code, but not, how you cll it, but the error is there.
x = [-10, 0, 10; -0.1, -1, 0];
matrixfx(x) % Working!
ans = 2×3
0 10.0000 20.0000 9.9000 9.0000 10.0000
function xout = matrixfx(xin)
xout = zeros(size(xin));
mask = xin > 0;
xout(mask) = xin(mask) * 2;
xout(~mask) = xin(~mask) + 10;
end

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