How do I make custom power trendline plots?

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HyoJae Lee
HyoJae Lee el 10 de Jul. de 2022
Comentada: Star Strider el 11 de Jul. de 2022
I have a question regarding to this answer.
The link is below:
I want to make a power fitting curve in the form of y=a*x^0.5+c.
However, the linked answer just provide full prediction of the fitting curve including exponent of the curve.
I want to fix the exponent as 0.5 or other value as a constant. Finally, I just want to figure out the number of a and c.
How do I revise the code in this case?
Thank you.

Respuesta aceptada

Star Strider
Star Strider el 10 de Jul. de 2022
Try something like this —
yfcn = @(b,x) b(1).*sqrt(x) + b(2);
x = 0:0.5:10;
y = rand(size(x));
[B,fval] = fminsearch(@(b) norm(y-yfcn(b,x)), rand(2,1))
B = 2×1
0.0233 0.4282
fval = 1.3888
xv = linspace(min(x), max(x));
yv = yfcn(B,xv);
figure
plot(x, y, '.')
hold on
plot(xv, yv, '-r')
hold off
grid
xlabel('X')
ylabel('Y')
title(sprintf('$y(x) = %.3f \\cdot \\sqrt{x} + %.3f$', B), 'Interpreter','latex')
NOTE — Using ‘sqrt(x)’ is computationally more efficient than ‘x.^0.5’.
.
  4 comentarios
HyoJae Lee
HyoJae Lee el 11 de Jul. de 2022
Last question! (sry...)
Is there any way to get r square value of the trendline?
Thanks!
Star Strider
Star Strider el 11 de Jul. de 2022
That would be easiest using the fitnlm function. It will do the fit and produce many relevant statistics, including the value.

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