How to define conditional function $f(x,y)$ with the following result. If $x=1$ and $y=0$ then $f=77$, if $x=0$ and $y=1$, then $f=66$, if $x$ and $y$ are all other integer values then $f=0$. How to define in Mathematica phrase 'all other values'?
f[x_,y_]:=Which[x==1 && y==0, 77,
x==0 && y==1, 66,
"all other values of x,y", 0]
I think it's easier just to define this straight up, rather than compute something procedurally.
f[1, 0] = 77;
f[0, 1] = 66;
f[_, _] = 0;
Mathematica is fundamentally an expression rewriting system, so telling it how to rewrite expressions directly like this is usually clearer, faster, and easier to debug.
f[_Integer, _Integer] and perhaps that's what @Timur would like. However, my answer meets his specification: he did not state what should happen for non-integers, and his attempt suggests 0 was a general default.
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Commented
Mar 15, 2018 at 14:15
f[x_Integer, y_Integer] :=Which[x == 1 && y == 0, 77, x == 0 && y == 1, 66, True, 0]
You can do this using Piecewise:
f[x_, y_] := Piecewise[{{77, {x, y} == {1, 0}}, {66, {x, y} == {0, 1}}}, 0]
(Piecewise takes as arguments an array of tupels {value,condition} and optionally a "default" value if all conditions are false.)
The null represents "all other values". You can replace it with anything you like.
f[x_, y_] := If[x == 1 && y == 0, 77, If[x == 0 && y == 1, 66, If[IntegerQ[x] && IntegerQ[y], 0, null]]]
Test it:
f[1, 0]
OUT: 77
f[0, 1]
OUT: 66
f[9, -2]
OUT: 0
f[9, 1.1]
OUT: null
f[1.2, Pi]
OUT: null
True? btw, what does&& ,mean, please pay attention. p.s.Switchwould be more handy here, take a look atPiecewisetoo. $\endgroup$,after&&. $\endgroup$