A small MATLAB function that allows you to quickly retrieve the relative differences between model outcomes and measurement values.

drdiff.m

function [ differences ] = drdiff(model_in, model_out, measured_in, measured_out)
%DRDIFF Discrete relative difference
%drdiff(model_in, model_out, measured_in, measured_out)
%Requirements:
%* model_in and model_out are two vectors of the same length
%* measured_in and measured_out are two vectors of the same length 
%
%Returns:
%A vector with the relative difference for each measurement point.


differences = [];

for i=1:length(measured_in)
    x = measured_in(i);
    
    d = sign(model_in - x); 
    
    for k=1:length(d)
        if (k ~= length(d))
            if (d(i) + d(k+1) == 0 || d(i) + d(k+1) == 1 || d(i) + d(k+1) == -1)
                boundA = k;
                boundB = k+1;
                break
            end
        end
    end
    
    slope = (model_out(boundB) - model_out(boundA))/(model_in(boundB) - model_in(boundA));
    
    approx = model_out(boundA) + slope*abs(x - model_in(boundA));
    relDiff = abs((measured_out(i) - approx)/approx);
    
    if (relDiff ~= Inf && ~isnan(relDiff))
        differences = [differences relDiff];
    end 
end
end