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2D interpolation


Hello,
 
I am asking (again) for your knowledge to help me.
I try to have a 2 dimensional interpolation of points {x, y, f(x,y)}.
After some try, I wrote these lines (as an exemple of what I want to do)
that works :
________________________________________

data = {{1, 1, -10}, {1, 2, 2}, {1, 3, 3}, {1, 4, 4}, {1, 5, 5}, {2, 1,
2}, {2, 2, 4}, {2, 3, 6}, {2, 4, 8}, {2, 5, 10}, {3., 1, -9}, {3, 2, 6},
{3, 3, 90}, {3, 4, 12}, {3, 5, 15}, {4, 1, 4}, {4, 2, 8}, {4, 3, 12},
{4, 4, 16}, {4, 5, 20}, {5, 1, 5}, {5, 2, 10}, {5, 3, 15}, {5, 4, 20},
{5, 5, 40.5}}; 

MatrixForm[data]

test[x_, y_] := Interpolation[data][x, y]; 

test[1.5, 1.5]

Plot[test[x, 1], {x, 1, 5}]; 

Plot[test[x, x], {x, 1, 5}]; 

Plot3D[test[x, y], {x, 1, 5}, {y, 1, 5}]; 

________________________________________
 
 
The problem is that when I want to use a point with a real x or y like
{1.23, 1.1, -10}, nothing works anymore.
I think that I miss something essential and fundamental, but I don'y
know why...
Thanks for your help,
Cheers,

Fabrice.


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