I should probably delete this question, since I found an answer elsewhere on stackoverflow.
Using 'Vectorize' solved the problem.
outer(x,y,Vectorize(model))
I'll leave this up for a bit in case this helps anyone else. The issue I had is described below.
I am an occasional user of R, mostly for Scientific Programming. I want to evaluate a function on a grid of x,y values. Something similar to this simple example:
> x=seq(1,5,1)
> y=seq(1,5,1)
> model = function(a,b){a+b}
> (outer(x,y,model))
[,1] [,2] [,3] [,4] [,5]
[1,] 2 3 4 5 6
[2,] 3 4 5 6 7
[3,] 4 5 6 7 8
[4,] 5 6 7 8 9
[5,] 6 7 8 9 10
The input and output of my actual function looks like this (the volumetric flow rate of a 'Cross' fluid in a circular pipe):
> SimpleCrossModelCircPipe(eta_0 = 176.45, lambda = 2.4526, m=0.83122, mesh=1000,
pipe_length=1.925, press_drop=20.3609, pipe_diameter=0.0413)
[1] 0.005635064
I want to evaluate the function on a grid of values, for example, press_drop and pipe_diameter. So, define a function of these two variables.
> model = function(a,b){SimpleCrossModelCircPipe(eta_0 = 176.45, lambda = 2.4526,
m=0.83122, mesh=1000,pipe_length=1.925, press_drop=a, pipe_diameter=b)}
For just one pair of values this does work:
> model(1,2)
[1] 107249.8
But, if I use with 'outer', there is an error.
> (outer(x,y,model))
Error in seq.default(tau_wall, 0, length.out = mesh + 1) : 'from' must be of length 1
If I place a print statement for the local variable, tau_wall, using outer generates all 25 values, before moving to the line, which generates the error, since tau_wall should have length 1, not 25.
(outer(x,y,model))
[1] 352.5289 705.0579 1057.5868 1410.1158 1762.6447 705.0579 1410.1158 2115.1736
[9] 2820.2315 3525.2894 1057.5868 2115.1736 3172.7605 4230.3473 5287.9341 1410.1158
[17] 2820.2315 4230.3473 5640.4630 7050.5788 1762.6447 3525.2894 5287.9341 7050.5788
[25] 8813.2235
Is there a simple fix to make this work?
Best,
Steve
