How to improve interpolation performance

Hi everyone,

I am using the shown function 'qinterplin1', which is much faster for my application cases. I'm only unhappy about some things:

• Performance
• Lots of 'if' queries

So here my questions:

• Are there any alternatives for the commented lines, requiring most of the time within the script?
• Is there a possibility to remove the differentation of "map_size"?

The input usually looks as foolowing:

x_vec = [25;80];
map = rand(2,4,4); % of course not random, but the numbers actually don't care
x_in = 25

or

x_vec = [1e-09,1e-08,2e-08,3e-08,4e-08,5e-08,6e-08,7e-08,8e-08,9e-08,1e-07,2e-07,3e-07,4e-07,5e-07,6e-07,7e-07,8e-07,9e-07,1e-06,0.001];
map = [0.0851,0.08510,0.07505,0.06510,0.05812,0.05111,0.04812,0.04512,0.04212,0.03913,0.03615,0.02038,0.04030,0.06520,0.08019,0.09129,0.1003,0.1103,0.12025,0.1302,0.1302];
x = 4.621e-9;

The script looks like this:

function [ret] = qinterplin1(x_vec, map, x)

map_size = ndims(map);
if map_size == 2
    if  any(size(map))==1 % 8.2% of time
        map_size = 1;
    end
end

use_dim = find(length(x_vec)==size(map)); % 10.4% of time

x(x<min(x_vec(:))) = min(x_vec(:)); % 17.1% of time
x(x>max(x_vec(:))) = max(x_vec(:)); % 13.9% of time


x0 = max(x_vec(x>=x_vec)); % 10.2% of time
x1 = min(x_vec(x<=x_vec));

if map_size==1

    if any(x==x_vec) && x0==x1
        ret = map(x_vec==x0);
        return;
    end
    
    y0 = map(x_vec==x0);
    y1 = map(x_vec==x1);
    
elseif map_size==2  && use_dim == 1
    
    if any(x==x_vec) && x0==x1
        ret = map(x_vec==x0);
        return;
    end
    
    y0 = map(x_vec==x0,:);
    y1 = map(x_vec==x1,:);
    
elseif map_size==3 && use_dim == 1

    if any(x==x_vec) && x0==x1
        ret = map(x_vec==x0,:,:);
        return;
    end
    
    y0 = map(x_vec==x0,:,:);
    y1 = map(x_vec==x1,:,:);
    
else
    error('this case needs to be programmed');
end

ret = y0 + (x-x0) * (y1-y0) / (x1-x0);

end

Thanks in advance & kind regards

Kevin

[Rik]

any(size(map))==1 %always returns true
any(size(map)==1) %doesn't always return true

You are calculating min(x_vec(:)) twice in one line, it might be worthwhile to calculate it once and store it in an intermediate variable.

temp=sort(x_vec(:));
x(x<temp(1)) = temp(1);
x(x>temp(end)) = temp(end);

For the rest I can't say much. Your function is too fast to reliably determine the time-consuming lines.