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60 lines
2.2 KiB
ReStructuredText
60 lines
2.2 KiB
ReStructuredText
.. highlight:: c
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.. _custom_expression:
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Custom Expressions
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-------------------------------------------------
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- Building custom expressions. The transpose example...
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Describe the concept, what to implement, etc....
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- Transpose::
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array<long,2> A (2,2), B(2,2),C(2,2);
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C= A + 2*B;
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C = A + Transpose(B); // Transpose(X) returns a lazy object that models HasImmutableArrayInterface.
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C = A + Transpose(B + B); // X can also be an expression...
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C = Transpose(B); //
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// non square
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array<long,2> R(2,3),Rt(3,2);
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cout<<" R = "<< array<long,2>(Transpose(R)) <<endl;
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// mapping any function
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C = map_expr(&sqr,A);
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cout<<" C = "<< map_expr(&sqr,A,"SQR")<<" = "<<C<<endl;
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// matmul as expression Oi are 'C' or 'F'
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matrix<double,O1> M1(2,2); matrix<double,O2> M2(2,2); matrix<double,O3> M3;
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// The central instruction : note that matmul returns a lazy object
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// that has ImmutableArray interface, and defines a specialized version assignment
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// As a result this is equivalent to some matmul_with_lapack(M1,M2,M3) : there is NO intermediate copy.
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M3 = matmul(M1,M2);
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See expression.hpp.
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At the moment, only +,-, * and / by scalar are implemented.
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An expression models HasImmutableArrayInterface, i.e. :
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* It has a domain (computed from the expression)
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* It can be evaluated.
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It is then easy to mix them with other objects,
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that model the same concept. See e.g. expr2.cpp (map_expr) for examples.
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* *Multiplication* :
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not decided, since it is not the same for array or matrices.
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Two choices :
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* Do not add \* for array, matrices (use matmul e.g.) and allow mixing array, matrix
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e.g. add an array<int,2> and a matrix <int>
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* Add the \*, but then do different expression for array and matrix/vector,
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then one can not mix them.
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In that case, it is however trivial to say e.g. M + matrix_view<int>(A) if A is an array.
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