It looks like the code that automatically does contractions is messing
with what you are trying to do here.
What I would try doing is using the sympy.codegen classes to construct
the loop you want. You can then print this directly using
contract=False to disable the automatic contraction. For example
>>> from sympy.codegen import For, CodeBlock, Assignment
>>> print(ccode(For(i, Range(m), CodeBlock(Assignment(K[i], M[i]*N[i]))),
>>> contract=False))
for (i = 0; i < m; i += 1) {
K[i] = M[i]*N[i];
}
Unfortunately, the sympy.utilities.codegen classes currently do not
know about the sympy.codegen classes. The idea is to eventually
replace everything with the sympy.codegen ast nodes.
Aaron Meurer
On Tue, Jun 13, 2023 at 12:45 AM Morten Olsen Lysgaard
<[email protected]> wrote:
>
> Ah, there is an inconsistency in the above email. I am saying I want
> dot-product, when in reality, what I want is an elementwise multiplication.
> The same question still applies though. Is this something Sympy can do?
>
> On Tuesday, 13 June 2023 at 06:28:52 UTC+2 Morten Olsen Lysgaard wrote:
>>
>> I am using Sympy for code generation.
>>
>> I would like to figure out the boundaries of what Sympy can do with respect
>> to code generation for dynamically sized arrays.
>>
>> Let's say I would like to generate a simple dot-product C-function.
>>
>> void dot(int m, const double *A, const double *B, double *C) {
>> for(int i=0; i<m; i++){
>> C[i] = A[i]*B[i];
>> }
>> }
>>
>> Using `sympy.Matrix` I am able to generate a loop-unrolled version of this
>> function for a fixed `m`, but this is not what I want. I want the general
>> thing.
>>
>> I have been trying to get this working using `IndexedBase` et. al. but no
>> luck. This is the closest I have gotten:
>>
>> import sys
>> import sympy as sp
>> import sympy.utilities.codegen
>> from sympy.utilities import codegen
>>
>> m = sp.symbols('m', integer=True)
>> i = sp.Idx('i', m)
>> M = sp.IndexedBase('M', shape=(m))
>> N = sp.IndexedBase('N', shape=(m))
>> K = sp.IndexedBase('K', shape=(m))
>> dot =sp.Eq(K[i], M[i]*N[i])
>>
>> rut_obj = codegen.make_routine('dot', dot, (m, M, N, K), language='C')
>> rcg = codegen.CCodeGen()
>> rcg.dump_c([rut_obj], sys.stdout, '')
>>
>> But it outputs spurious loops which I can not explain, and will not compute
>> the correct answer:
>>
>> void dot(int m, double *M, double *N, double *K) {
>> for (int i=0; i<m; i++){
>> K[i] = 0;
>> }
>> for (int i=0; i<m; i++){
>> for (int i=0; i<m; i++){
>> K[i] = K[i] + M[i]*N[i];
>> }
>> }
>> }
>>
>> Is there anyone that are able to generate a simple dot-product function like
>> the one in the top of my email using Sympy code generation?
>>
>> Any help would be greatly appreciated!
>
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