sparse matrix

I am trying out to form a sparse matrix but it runs out of memory.Below is the code similar to which I have been working on A=sparse(15000,15000); inb=sparse(eye(10000,10000); it goes out of memory here.

So for forming a identity matrix (inb) I use: inb=sparse(10000,10000); for i=1:1:10000; inb(i,i)=ones; end A(1:10000,1:10000)=inb; it goes out of memory. Is there any way I can get rid of this.

Answer 1

[Andrei Bobrov]

blkdiag(speye(30886,30886),sparse(68709-30886,130478-30886));

[Samir]

Thanks Andrei.

Answer 2

[the cyclist]

Try the speye() command.

[Samir]

Thanks speye() works fine but when assigning it back to a sparse matrix it goes out of memeory like:

A=sparse(15000,15000);

inb=speye(10000,10000);

A(1:10000,1:10000)=inb;

After the third line it goes out of memory

[the cyclist]

I have no problem running that code, and it results in the sparse arrays I expect.

[Samir]

Thanks the cyclist it worked on the computer with high ram.

but actually my this is the real case could you suggest any better option for the following:

aeq=sparse(68709,130478);

inb=speye(30886,30886);

aeq(1:30886,1:30886)=inb;

This is running out of memory now.

I am not getting why MATLAB is not able to include the identity matrix after being sparse also.

Is there any way I can check the number of elements I can include in the array.

Answer 3

[Walter Roberson]

aeq=sparse(68709,130478);

generates an empty 68709 by 130478 sparse matrix, with the number of expected non-zero elements set to 0. But then you set a whole bunch of elements to non-zero, which requires reorganizing the sparse matrix as it detects more and more non-zero elements.

If you were to use

aeq=sparse([], [], [], 68709,130478, 30886);

then it would probably have less difficulty.

[Samir]

Thankyou but still the same issue:

>> aeq=sparse([], [], [], 68709,130478, 30886);

>> aeq(1:30886,1:30886)=speye(30886,30886);

??? Out of memory. Type HELP MEMORY for your options.

Answer 4

[Rahul Pal]

function y = caesar2(ch, key)

v = ' ' : '~';

[~, loc] = ismember(ch, v);

v2 = circshift(v, -key);

y = v2(loc);

end