Write a function named custom_blocks

Write a function named custom_blocks that takes an n-by-m

matrix as an input argument (the function does not have to check the format

of the input) and returns a 2n-by-2m matrix as an output argument. The upper

left n-by-m sub matrix of the output matrix is the same as the input matrix.

The elements of the upper right n-by-m sub matrix are twice as large as

the corresponding elements of the input matrix. Similarly, the lower left submatrix

is the input matrix multiplied by three and the lower right n-by-m submatrix

is four times the input matrix. For example, here is an example run:

>> custom_blocks([1:3;3:-1:1])

ans =

1 2 3 2 4 6

3 2 1 6 4 2

3 6 9 4 8 12

9 6 3 12 8 4

[Siddharth Varshney]

My code is incorrect. can someone give a hint for this question?

My code is:-

function A = cancel_middle1(n,m)
A((1:n),(m+1:m*2))*2;
A((n+1:n*2),(1:m))*3;
A((n+1:n*2),(m+1:m*2))*4;
end

[Walter Roberson]

Where are you assigning anything to A? You index into it to pull values out of it, and you do minor arithmetic and then you discard the results of the calculation... but first you need to have an A array to index into

[Siddharth Varshney]

No its still showing:-

Error in cancel_middle1 (line 3)

A((1:n),(m+1:m*2))*2;

[Siddharth Varshney]

Please can you tell me the value i should assign to A?

[Walter Roberson]

You should be using code of the general form

A(rows, columns) = array of values

You currently have the A(rows, columns) part but not the assignment or the right hand side

[Siddharth Varshney]

Is this correct?

function A  = cancel_middle1(n,m)
A(1:n,1:m)=1;
A(1:n,m+1:m*2)= 2;
A(n+1:n*2,1:m)= 3;
A(n+1:n*2,m+1:m*2)=4;
end

[Steven Lord]

Does your function satisfy the requirements given in the problem statement? [No, it does not. What does the assignment say your function needs to accept as the input?]

When you try to reproduce the results from the example given in the problem, can you?

I recommend copying each sentence of the problem statement as comments and then writing the code to perform each of those steps. Fill in the blanks.

% List the input(s) and output(s) of your function
function fill_in_this_blank = cancel_middle(fill_in_this_blank)

% The upper left n-by-m sub matrix of the output matrix is the same as the input matrix.
fill_in_this_blank

% The elements of the upper right n-by-m sub matrix are twice as large as the
% corresponding elements of the input matrix.
fill_in_this_blank

% Similarly, the lower left submatrix is the input matrix multiplied by three
fill_in_this_blank

% and the lower right n-by-m submatrix is four times the input matrix.
fill_in_this_blank

end

[Walter Roberson]

The problem does not pass in the values of m and n . The problem passes in a matrix with a particular number of rows and a particular number of columns. If you call the number of rows received n, and the number of columns received m, then the number of rows out must be 2*n and the number of columns out must be 2*m -- that is, the output must have twice as many rows as the input, and twice as many columns as the input.

[Stephen23]

https://web.archive.org/save/https://www.mathworks.com/matlabcentral/answers/1604015-write-a-function-named-custom_blocks

Answer 1

[Voss]

function out = custom_blocks(in)
    out = [in 2*in; 3*in 4*in];
end

[Walter Roberson]

Please note that this is a homework problem.

[Voss]

Please note that I am aware of that and answered it anyway.

[Walter Roberson]

The experience of the long-time volunteers is that it is most often better to guide students into how to read questions, and how to find resources, rather than to give them exact solutions to problems. In cases where specific code is useful, it is our experience that is often better to give code for a different question that uses the same principles, so that the student at least has to recognize the principles.

[Voss]

I appreciate your comments. In the future, I will take the approach of solving a similar question that uses the same principles, as you suggest.