How do create a loglog line of best fit?
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Nicholas Green
el 23 de Sept. de 2015
Comentada: Star Strider
el 16 de Nov. de 2022
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)
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Respuesta aceptada
Star Strider
el 23 de Sept. de 2015
Try this:
Const = polyfit(log(temp),log(density), 1)
m = Const(1)
k = Const(2)
YBL = x.^m.*exp(k)
19 comentarios
Les Beckham
el 16 de Nov. de 2022
I guess I should have emphasized that point more than with the cursory sentences "Be careful of using points that aren't spanned by the range of the original fit. Extrapolation can be dangerous (give you misleading results)."
Star Strider
el 16 de Nov. de 2022
@Les Beckham — Thank you!
I thought the concept needed an illustration, so I provided one.
Más respuestas (1)
Walter Roberson
el 23 de Sept. de 2015
logx = log(temp);
logy = log(density);
Const = polyfit(logx, logy, 1)
hold on
plot(temp, exp(polyval(Const, logx)));
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