The lagrange command finds the Lagrange
polynomial which interpolates given data.
interp is a synonym for lagrange.
Examples.
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Warning.
An attempted function definition such as
f:=lagrange([1,2],[3,4],y) does not return a function but an
expression with respect to y. To define f as a function, input:
Avoid f(x):=lagrange([1,2],[3,4],x) since then the Lagrange polynomial would be computed each time f is called (indeed in a function definition, the second member of the assignment is not evaluated). Note also that g(x):=lagrange([1,2],[3,4]) would not work since the default argument of lagrange would be global, hence not the same as the local variable used for the definition of g.