Why does mldivide() run fine on system A, but run out of memory on system B, when system B has *more* memory than system A?

My problem requires I solve a system of the form M*x=b, where M and b are generated in a separate program and read-in when the MATLAB program starts. M is complex, large square (~1,000,000 x 1,000,000), and sparse. I am running the code on a high-performance Linux node at a supercomputer cluster. When I moved to larger problems, I found that I was running out of memory on the 128GB nodes, so I moved my code to the large memory nodes, where an arbitrary (up to the total available memory of 1.5TB) memory limit can be requested. Surprisingly, I found that the same mldivide code that ran perfectly on the standard node ran out of memory on the large memory node. I suspect that MATLAB's memory management sees the full 1.5TB memory, and is more liberal with its memory usage, and less aggressive about clearing up memory, leading to the code hitting the (lower) set memory limit. Because I am charged by the percentage of the 1.5TB of memory I request, simply requesting 100% of the memory is not a realistic option if i am not actually using all of it. How can I solve this issue? Thanks.

[Walter Roberson]

What is set in your Preferences for Maximum Array Size?

[Daniel Walsh]

I am using MATLAB through the command line; I don't believe such an option exists. In any event, I don't believe this is an issue, as the code was run with no upper bound on memory, and successfully finished, using ~210GB of memory.

[Walter Roberson]

You indicated that you moved to larger memory nodes; was that through some kind of remote submission from the same starting point, or was it by executing MATLAB from different starting points?

Just trying to check against the possibility of a slightly different MATLAB configuration.

[Walter Roberson]

In your prefdir, with modern MATLAB, look for matlab.settings and search in it for the key ArraySizeLimitEnabled which will be 0 if array size is unlimited and 1 if the limit is to be applied.

[Daniel Walsh]

Thanks Walter, I checked the settings and the ArraySizeLimitEnabled is set to 1:

       <key name="ArraySizeLimitEnabled" visible="true">
         <bool>
           <value>1</value>
         </bool>
       </key>

(this was in workspace.settings though - not matlab.settings).

What do you make of this?

[Walter Roberson]

It might be the problem. I am far from certain that it is the cause of the difficulty you are seeing, but it is the most obvious knob to frob to try to fix the issue.