Matrix multiplication: Difference between revisions

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 =={{header|J}}==
-Matrix multiply in J is just <tt>+/ .*</tt>.  For example:
+Matrix multiply in J is just <code>+/ .*</code>.  For example:
+<lang j>
-    x  =:  +/ .*
+   mp  =:  +/ .*      NB.  Matrix product
-    A  =:  ^/~>:i. 4   NB.  Same  A  as in other examples (1 1 1 1, 2 4 8 16, 3 9 27 81,:4 16 64 256)
-    B  =:  %.A         NB.  Matrix inverse of A
-    '6.2' 8!:2 A x B
-.00  0.00  0.00  0.00
-.00  1.00  0.00  0.00
-.00  0.00  1.00  0.00
-.00  0.00  0.00  1.00
+   A  =:  ^/~>:i. 4   NB.  Same  A  as in other examples (1 1 1 1, 2 4 8 16, 3 9 27 81,:4 16 64 256)
+   B  =:  %.A         NB.  Matrix inverse of A
+   '6.2' 8!:2 A mp B
+.00  0.00  0.00  0.00
+.00  1.00  0.00  0.00
+.00  0.00  1.00  0.00
+.00  0.00  0.00  1.00
+</lang>
 The notation is for a generalized inner product so that
+<lang j>
-    x ~:/ .*. y   NB. boolean inner product (<tt>~: </tt>is "not equal" (exclusive or) and<tt> *. </tt>is "and")
-    x *./ .=  y   NB. which rows of x are the same as vector y?
+   x ~:/ .*. y   NB. boolean inner product (<tt>~: </tt>is "not equal" (exclusive or) and<tt> *. </tt>is "and")
-    x + / .=  y   NB. number of places where each row of x equals vector y
+   x *./ .=  y   NB. which rows of x are the same as vector y?
+   x + / .=  y   NB. number of places where each row of x equals vector y
+</lang>
 etc.