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Plot the following custom function?

Posted 7 months ago
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I am trying to plot this function with Plot3D and ContourPlot and they both give blank boxes. Is there something wrong with my code?

f[x_, y_] =  4*Sin[x - 2] + 4*Cos[y - 4] + 9*x^2 - 5*xy + 1*y^2 - 2*x + 4*y
4 Replies
Posted 7 months ago

Try

f[x_, y_] := 4Sin[x - 2] + 4Cos[y - 4] + 9x^2 - 5x*y + 1y^2 - 2x + 4*y ;
Plot3D[f[x,y],{x,-Pi,Pi},{y,-Pi,Pi}]
Posted 7 months ago

Hi Katelyn,

You did not post the code you tried so it is not possible to identify what is wrong with it.

f[x_, y_] := 4 Sin[x - 2] + 4 Cos[y - 4] + 9 x^2 - 5 x y + 1 y^2 - 2 x + 4*y
Plot3D[Evaluate@f[x, y], {x, -2 Pi, 2 Pi}, {y, -2 Pi, 2 Pi}]

enter image description here

Note that including Evaluate in the Plot expression cuts the time roughly in half (on my system, from around 0.293 sec to around 0.017 sec).

This should hardly matter — except, say, if you were going to be changing the function or the plot range dynamically within a Manipulate.

I suggest you use the delayed evaluation ":=". For example,If we set x=1;the define a function x+2 with direct assignment and delayed assignment,respectively.The following answer we will get.

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