Maxima Function
outermap (f, a_1, ..., a_n)
Applies the function f to each one of the elements of the outer product a_1 cross a_2 ... cross a_n.
f is the name of a function of n arguments or a lambda expression of n arguments. Each argument a_k may be a list or nested list, or a matrix, or any other kind of expression.
The outermap
return value is a nested structure.
Let x be the return value.
Then x has the same structure as the first list, nested list, or matrix argument,
x[i_1]...[i_m]
has the same structure as the second list, nested list, or matrix argument,
x[i_1]...[i_m][j_1]...[j_n]
has the same structure as the third list, nested list, or matrix argument,
and so on,
where m, n, ... are the numbers of indices required to access the
elements of each argument (one for a list, two for a matrix, one or more for a nested list).
Arguments which are not lists or matrices have no effect on the structure of the return value.
Note that the effect of outermap
is different from that of applying f
to each one of the elements of the outer product returned by cartesian_product
.
outermap
preserves the structure of the arguments in the return value,
while cartesian_product
does not.
outermap
evaluates its arguments.
Examples:
Elementary examples of outermap
.
To show the argument combinations more clearly, F
is left undefined.
(%i1) outermap(F, [a, b, c], [1, 2, 3]); (%o1) [[F(a, 1), F(a, 2), F(a, 3)], [F(b, 1), F(b, 2), F(b, 3)], [F(c, 1), F(c, 2), F(c, 3)]] (%i2) outermap(F, matrix([a, b],[c, d]), matrix([1, 2],[3, 4])); [ [ F(a, 1) F(a, 2) ] [ F(b, 1) F(b, 2) ] ] [ [ ] [ ] ] [ [ F(a, 3) F(a, 4) ] [ F(b, 3) F(b, 4) ] ] (%o2) [ ] [ [ F(c, 1) F(c, 2) ] [ F(d, 1) F(d, 2) ] ] [ [ ] [ ] ] [ [ F(c, 3) F(c, 4) ] [ F(d, 3) F(d, 4) ] ] (%i3) outermap (F, [a, b], x, matrix ([1, 2], [3, 4])); [ F(a, x, 1) F(a, x, 2) ] [ F(b, x, 1) F(b, x, 2) ] (%o3) [[ ], [ ]] [ F(a, x, 3) F(a, x, 4) ] [ F(b, x, 3) F(b, x, 4) ] (%i4) outermap (F, [a, b], matrix ([1, 2]), matrix ([x], [y])); [ [ F(a, 1, x) ] [ F(a, 2, x) ] ] (%o4) [[ [ ] [ ] ], [ [ F(a, 1, y) ] [ F(a, 2, y) ] ] [ [ F(b, 1, x) ] [ F(b, 2, x) ] ] [ [ ] [ ] ]] [ [ F(b, 1, y) ] [ F(b, 2, y) ] ] (%i5) outermap ("+", [a, b, c], [1, 2, 3]); (%o5) [[a + 1, a + 2, a + 3], [b + 1, b + 2, b + 3], [c + 1, c + 2, c + 3]]
A closer examination of the outermap
return value.
The first, second, and third arguments are a matrix, a list, and a matrix, respectively.
The return value is a matrix.
Each element of that matrix is a list,
and each element of each list is a matrix.
(%i1) arg_1 : matrix ([a, b], [c, d]); [ a b ] (%o1) [ ] [ c d ] (%i2) arg_2 : [11, 22]; (%o2) [11, 22] (%i3) arg_3 : matrix ([xx, yy]); (%o3) [ xx yy ] (%i4) xx_0 : outermap(lambda([x, y, z], x / y + z), arg_1, arg_2, arg_3); [ [ a a ] [ a a ] ] [ [[ xx + -- yy + -- ], [ xx + -- yy + -- ]] ] [ [ 11 11 ] [ 22 22 ] ] (%o4) Col 1 = [ ] [ [ c c ] [ c c ] ] [ [[ xx + -- yy + -- ], [ xx + -- yy + -- ]] ] [ [ 11 11 ] [ 22 22 ] ] [ [ b b ] [ b b ] ] [ [[ xx + -- yy + -- ], [ xx + -- yy + -- ]] ] [ [ 11 11 ] [ 22 22 ] ] Col 2 = [ ] [ [ d d ] [ d d ] ] [ [[ xx + -- yy + -- ], [ xx + -- yy + -- ]] ] [ [ 11 11 ] [ 22 22 ] ] (%i5) xx_1 : xx_0 [1][1]; [ a a ] [ a a ] (%o5) [[ xx + -- yy + -- ], [ xx + -- yy + -- ]] [ 11 11 ] [ 22 22 ] (%i6) xx_2 : xx_0 [1][1] [1]; [ a a ] (%o6) [ xx + -- yy + -- ] [ 11 11 ] (%i7) xx_3 : xx_0 [1][1] [1] [1][1]; a (%o7) xx + -- 11 (%i8) [op (arg_1), op (arg_2), op (arg_3)]; (%o8) [matrix, [, matrix] (%i9) [op (xx_0), op (xx_1), op (xx_2)]; (%o9) [matrix, [, matrix]
outermap
preserves the structure of the arguments in the return value,
while cartesian_product
does not.
(%i1) outermap (F, [a, b, c], [1, 2, 3]); (%o1) [[F(a, 1), F(a, 2), F(a, 3)], [F(b, 1), F(b, 2), F(b, 3)], [F(c, 1), F(c, 2), F(c, 3)]] (%i2) setify (flatten (%)); (%o2) {F(a, 1), F(a, 2), F(a, 3), F(b, 1), F(b, 2), F(b, 3), F(c, 1), F(c, 2), F(c, 3)} (%i3) map(lambda([L], apply(F, L)), cartesian_product({a, b, c}, {1, 2, 3})); (%o3) {F(a, 1), F(a, 2), F(a, 3), F(b, 1), F(b, 2), F(b, 3), F(c, 1), F(c, 2), F(c, 3)} (%i4) is (equal (%, %th (2))); (%o4) true