I'm multiplying 2 3x3 matrices and the answer is displaying as a 1x9, how can i fix this?

Question

Terry Poole 2018-10-8

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评论： Star Strider 2018-10-8

A=[0.4 0.1 0.2;0.3 0.7 0.7;0.3 0.2 0.1];
b=[0.4 0.1 0.2;0.3 0.7 0.7;0.3 0.2 0.1];
for i = 1:40
 b = A*b;
 fprintf('i=%3d b=[',i);
 for j = 1:9
 fprintf('%12.6f',b(j));
 end
 fprintf(']\n');
end

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Answer 1

Star Strider 2018-10-8

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Your code is printing what you told it to print.

Try this:

A=[0.4 0.1 0.2;0.3 0.7 0.7;0.3 0.2 0.1];
b=[0.4 0.1 0.2;0.3 0.7 0.7;0.3 0.2 0.1];
for i = 1:40
    b = A*b;
    fprintf('i=%3d b=[',i);
    fprintf('%12.6f %12.6f %12.6f\n%12.6f %12.6f %12.6f\n%12.6f %12.6f %12.6f',b');
    fprintf(']\n');
end

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Terry Poole 2018-10-8

That did it!!! Sorry, I'm terribly new to Matlab. I knew it was somthing inside the for loop, I actually tried the %12.6f multiple times to declare the row's/columns it didn't occur to me to remove the J all together, I assumed I needed to declare a new letter to define the answer of A*b to the ith iteration. Thank you so much!!!

Star Strider 2018-10-8

As always, my pleasure!

No apologies necessary. We were all new to MATLAB (and to programming in general) at one point in our lives. We’re all still learning.

The solution is in understanding how fprintf (and sprintf) intrepret matrix arguments. It’s worthwhile experimenting with it when time permits.

It is quite understandable that you would consider the need to subscript your matrix so it prints the way you want it to, however since you have already defined your matrix, printing it is relatively straightforward.

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