Handling Large mxArrays

Binary MEX files built on 64-bit platforms can handle 64-bit mxArrays. These large data arrays can have up to 2⁴⁸–1 elements. The maximum number of elements a sparse mxArray can have is 2⁴⁸-2.

Using the following instructions creates platform-independent binary MEX files as well.

Your system configuration can affect the performance of MATLAB^®. The 64-bit processor requirement enables you to create the mxArray and access data in it. However, the system memory, in particular the size of RAM and virtual memory, determine the speed at which MATLAB processes the mxArray. The more memory available, the faster the processing.

The amount of RAM also limits the amount of data you can process at one time in MATLAB. For guidance on memory issues, see Strategies for Efficient Use of Memory.

Using the 64-Bit API

The signatures of the API functions shown in the following table use the mwSize or mwIndex types to work with a 64-bit mxArray. The variables you use in your source code to call these functions must be the correct type.

Fortran mxArray Functions Using mwSize/mwIndex

mxCalcSingleSubscript	mxCreateStructMatrix
mxCalloc	mxGetCell
mxCopyCharacterToPtr	mxGetDimensions
mxCopyComplex16ToPtr	mxGetElementSize
mxCopyComplex8ToPtr	mxGetField
mxCopyInteger1ToPtr	mxGetFieldByNumber
mxCopyInteger2ToPtr	mxGetIr
mxCopyInteger4ToPtr	mxGetJc
mxCopyPtrToCharacter	mxGetM
mxCopyPtrToComplex16	mxGetN
mxCopyPtrToComplex8	mxGetNumberOfDimensions
mxCopyPtrToInteger1	mxGetNumberOfElements
mxCopyPtrToInteger2	mxGetNzmax
mxCopyPtrToInteger4	mxGetProperty
mxCopyPtrToPtrArray	mxGetString
mxCopyPtrToReal4	mxMalloc
mxCopyPtrToReal8	mxRealloc
mxCopyReal4ToPtr	mxSetCell
mxCopyReal8ToPtr	mxSetDimensions
mxCreateCellArray	mxSetField
mxCreateCellMatrix	mxSetFieldByNumber
mxCreateCharArray	mxSetIr
mxCreateCharMatrixFromStrings	mxSetJc
mxCreateDoubleMatrix	mxSetM
mxCreateNumericArray	mxSetN
mxCreateNumericMatrix	mxSetNzmax
mxCreateSparse	mxSetProperty
mxCreateStructArray

Caution Using Negative Values

When using the 64-bit API, mwSize and mwIndex are equivalent to INTEGER*8 in Fortran. This type is unsigned, unlike INTEGER*4, which is the type used in the 32-bit API. Be careful not to pass any negative values to functions that take mwSize or mwIndex arguments. Do not cast negative INTEGER*4 values to mwSize or mwIndex; the returned value cannot be predicted. Instead, change your code to avoid using negative values.

Building Cross-Platform Applications

If you develop cross-platform applications (programs that can run on both 32-bit and 64-bit architectures), pay attention to the upper limit of values you use for mwSize and mwIndex. The 32-bit application reads these values and assigns them to variables declared as INTEGER*4 in Fortran. Be careful to avoid assigning a large mwSize or mwIndex value to an INTEGER*4 or other variable that might be too small.