MATLAB: How do create a loglog line of best fit

line of best fitloglog

So far I've plotted my data and found that a loglog plot gives the most linear result. The line of best fit, however, isn't linear. How do i fix it? It also displays "negative numbers ignored" which might tie into it.
%%HK
close all % closes all windows
clear all % clae all variables
clc % clear command windows
beep off % turn beep noise off
format compact % tight spacing 
%%Data
temp = [100,200,400,600,800,1000,1200,1400,1600]
density = [3.5,1.7,0.85,0.6,0.45,0.35,0.3,0.25,0.2]
%%Plot
loglog(temp, density, '*')
xlabel('Temperature T,K')
ylabel('Density D, kg/m^3')
title('Temperature vs. Density')
grid on
%%Equation constants
Const = polyfit(temp,density, 1)
m = Const(1)
k = Const(2)
%%Bestfit Line
hold on
YBL = m*temp+k
loglog(temp,YBL)

Best Answer

Try this:
Const = polyfit(log(temp),log(density), 1)
m = Const(1)
k = Const(2)
YBL = x.^m.*exp(k)
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