# How to solve the problem Ax=b, when A is (14400,14400) and b (14400,1)?

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When I try to solve this problem with x=A\b or rref a message saying "Out of memory" is shown.

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### Answers (3)

Star Strider
on 27 Jan 2015

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Star Strider
on 29 Jan 2015

John D'Errico
on 27 Jan 2015

This is not that huge of a problem.

If your matrix is sparse and you are not storing it as such (as matrices of that size are so frequently sparse on these problems) then why are you not using a sparse form?

Have you tried using an iterative solver? There are several of them to be found in MATLAB, LSQR for example.

Finally, make sure you have sufficient memory, AND you are using a current release of MATLAB, which will use 64 bit addressing.

Problems with 14k unknowns are simply not that difficult to solve anymore, so you need to explain more about what you are doing, and what you are doing wrong.

Matz Johansson Bergström
on 27 Jan 2015

If A is full \ has to perform a Gaussian elimination. A is ~1.5GB in double precision and it seems that \ requires at least that amount of RAM during GE.

How much RAM do you have?

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