RE: Function defined with If

*To*: mathgroup at smc.vnet.net*Subject*: [mg71382] RE: [mg71338] Function defined with If*From*: "David Park" <djmp at earthlink.net>*Date*: Thu, 16 Nov 2006 00:53:24 -0500 (EST)

Julián, I'm not quite certain what you want to do. Suppose that a and b are complicated expressions of x and y. Do you want f to be a function of x and y, or of a and b? I am going to assume a function of x and y. Then note the Attributes of If. Attributes[If] {HoldRest, Protected} So in the f definition we have to evaluate the second and third arguments of If. a = x; b = y; f[x_, y_] = If[a < b, Evaluate@a, Evaluate@b] If[x < y, x, y] David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: Julian Aguirre [mailto:julian.aguirre at ehu.es] Dear group, I am trying to define a function of the variables x, y through other quantities depending on x and y and the function If. A minimal example is In[1]:a = x; b = y; f[ x_, y_ ] = If[ a < b, a, b ] Out[3]If[ x < y, a, b ] How can I force Mathematica to return If[ x < y, x, y ], as I thought it would? Thaks in advance, Julián Aguirre