Unsatisfied answer and no errors

Hi,

I am new to the Matlab and I want to develop a 10X10X10 voxel(cube) function programme and set all the voxels on the edges "1" and rest(internal voxels)as "0". Then I have to develop a function to calculate the ratio of "1" and "0" and validate my answer using the hand calculations. I have developed a function to find the voxels on the edges(1) and rest as (0).but i am not satisfied with my answer. there is no error.but the answer is wrong(sum of the voxels on the edges and sum of the internal voxels are wrong). I have selected i,j,k values that matches with the voxels on the edges(1) and internal voxels(0) as below programme written by me using the hand skethced diagram.Appreciate your comments.

b=zeros(10,10,10);

for i=1:10

for j=1:10

for k=1:10

if ((i ==1) || (i==2) || (i==3)||(i==4)||(i==5)||(i ==6) || (i==7) || (i==8)||(i==9)||(i==10)) && ((j==1) || (j==10)) && ((k==1) || (k==10))

b(i,j,k)=1;

else

b(i,j,k)=0;

if ((i ==1) || (i==10)) && ((j==2) || (j==3) || (j==4)||(j==5) || (j==6) || (j==7)||(j==8) || (j==9)) &&( (k==1) || (k==10))

b(i,j,k)=1;

else

b(i,j,k)=0;

if ((i ==1) || (i==10)) && ((k==2) || (k==3) || (k==4)|| (k==5) || (k==6) || (k==7)||(k==8) || (k==9)) && ((j==1) || (j==10))

b(i,j,k)=1;

else

b(i,j,k)=0;

end

end

end

end

end

end

sum b(i,j,k)=1

sum b(i,j,k)=0

note---sum b(i,j,k)=1 shown as 695 and sum b(i,j,k)=0 shown as 694 which is totally wrong.(695+694 is not equal to 10X10X10)

Answer 1

[Steven Lord]

sum b(i,j,k)=1
sum b(i,j,k)=0

These lines don't do what you think they do. They are equivalent to:

sum('b(i,j,k)=1')
sum('b(i,j,k)=0')

which means they're adding up the ASCII values of the characters in those two char vectors.

There's an easier way to create your desired array. Let's start off with a 10-by-10-by-10 array filled with 0's just as you did.

A = zeros(10, 10, 10);

Now, for all the columns and pages of A, we want to fill in rows 1 and 10 with the value 1. This uses array indexing with element positions. When you read this, read : as "all".

A([1 10], :, :) = 1; % Elements in rows 1 and 10, all columns, all pages of A

We do the same for all rows and pages of A, filling in columns 1 and 10.

A(:, [1 10], :) = 1; % Elements in all rows, columns 1 and 10, all pages of A

And the same for all rows and columns, filling in pages 1 and 10.

A(:, :, [1 10]) = 1; % Elements in all rows, all columns, pages 1 and 10 of A

Now if we've done it right, A should have an 8-by-8-by-8 array of 0's still in the middle. Let's make sure it has the right number of 0's.

nnz(A == 0) % 512 == 8*8*8

The only other values in A are an outer "shell" of 1's.

nnz(A == 1) % 1000 - 512 = 488

[Hege]

Hi Steven, Thank you very much for your help.I really appreciate it.