Multivariate Functions with Conditions in Mathematica

Question

I'm trying to define a bivariate function that takes values depending on whether a condition is met. I make them work for univariate case but I'm stuck with the bivariate case:

g[x_, y_] := 10 /; x < 10
g[x_, y_] := 20 /; (x >= 10 && y < 5)
g[x_, y_] := -5 /; (x >= 10 && y >= 5);

This function never gives me the value of -5.

g[12,10] = 20?

Your definition works fine and Mark's answer is no different from yours. You probably had a previous definition for g and clearing it helped. — abcd
– abcd, Commented Jan 29, 2013 at 2:07
Yes indeed, OP's definition of g works fine. Now. Strange thing is that when I tried it in a fresh Mathematica session last night the definitions returned $Failed. — High Performance Mark
– High Performance Mark, Commented Jan 29, 2013 at 6:54

High Performance Mark · Accepted Answer · 2013-01-28 22:15:18Z

2

This works for me:

Clear[g]
g[x_, y_] /; x < 10 := 10
g[x_, y_] /; x >= 10 \[And] y < 5 := 20
g[x_, y_] /; x >= 10 \[And] y >= 5 := -5

then

In[73]:= g[12, 10]

Out[73]= -5

Why this version works and your version doesn't I'm not sure. Perhaps someone else will come along and tell us

answered Jan 28, 2013 at 22:15

High Performance Mark

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1 Comment

user950899 Over a year ago

Thank you Mark. Works perfecly.

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