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Enable large arrays: Build octave such that it can use arrays larger than 2Gb.: Difference between revisions
Enable large arrays: Build octave such that it can use arrays larger than 2Gb. (edit)
Revision as of 06:05, 29 August 2019
, 29 August 2019Add an example to see the effect of using BLAS libraries with either 32 or 64 bit indices.
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(Add an example to see the effect of using BLAS libraries with either 32 or 64 bit indices.) |
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* glpk | * glpk | ||
* Qhull | * Qhull | ||
To determine the integer size of the BLAS library used by Octave run one of the following lines: | |||
<syntaxhighlight lang="Octave"> | |||
clear all; N = 2^31; a = b = ones (N, 1, "single"); c = a' * b # ~ 8 GB RAM required! | |||
clear all; N = 2^31; a = b = ones (N, 1); c = a' * b # ~16 GB RAM required! | |||
</syntaxhighlight> | |||
If the BLAS library uses '''32-bit integers''', an error will be thrown in both cases: | |||
error: integer dimension or index out of range for Fortran INTEGER type | |||
Otherwise, if the BLAS library uses '''64-bit integers''', the result is: | |||
c = 2^31 = 2147483648 | |||
Note that the two test cases above would usually require twice the memory, if <code>a</code> and <code>b</code> differ and are not assigned by <code>a = b = ...</code>. | |||
Note further, that the single precision data type has a precision of about 23 binary bits. | |||
In this particular example no rounding errors occur. | |||
===Versions prior to Octave 4.4=== | ===Versions prior to Octave 4.4=== | ||
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With this option, Octave will use internally 64-bit integers for array dimensions and indexing. However, '''all numerical libraries''' used by Octave will need to use also 64-bit integers for array dimensions and indexing, and in most cases they need to be compiled from source. | With this option, Octave will use internally 64-bit integers for array dimensions and indexing. However, '''all numerical libraries''' used by Octave will need to use also 64-bit integers for array dimensions and indexing, and in most cases they need to be compiled from source. | ||
For details about how to compile these libraries please read the [http://www.gnu.org/software/octave/doc/interpreter/Compiling-Octave-with-64_002dbit-Indexing.html#Compiling-Octave-with-64_002dbit-Indexing GNU Octave manual], or alternatively you can use [ | For details about how to compile these libraries please read the [http://www.gnu.org/software/octave/doc/interpreter/Compiling-Octave-with-64_002dbit-Indexing.html#Compiling-Octave-with-64_002dbit-Indexing GNU Octave manual], or alternatively you can use [[MXE]] (M Cross Environment) which takes care of the different packages automatically (especially the configure flags <code>--enable-64</code> and <code>--enable-fortran-int64</code>). | ||
[[Category:Building]] | [[Category:Building]] | ||