---

11.56 Sample ‘fit’ ¶

Example of nonlinear fit.

MGL code:

new dat 100 '0.4*rnd+0.1+sin(2*pi*x)'
new in 100 '0.3+sin(2*pi*x)'
list ini 1 1 3:fit res dat 'a+b*sin(c*x)' 'abc' ini
title 'Fitting sample':yrange -2 2:box:axis:plot dat 'k. '
plot res 'r':plot in 'b'
text -0.9 -1.3 'fitted:' 'r:L'
putsfit 0 -1.8 'y = ' 'r':text 0 2.2 'initial: y = 0.3+sin(2\pi x)' 'b'

C++ code:

void smgl_fit(mglGraph *gr)	// nonlinear fitting
{
	mglData dat(100), in(100), res;
	gr->Fill(dat,"0.4*rnd+0.1+sin(2*pi*x)");
	gr->Fill(in,"0.3+sin(2*pi*x)");
	double ini[3] = {1,1,3};
	mglData Ini(3,ini);
	res = gr->Fit(dat, "a+b*sin(c*x)", "abc", Ini);
	if(big!=3)	gr->Title("Fitting sample");
	gr->SetRange('y',-2,2);	gr->Box();	gr->Plot(dat, "k. ");
	gr->Axis();		gr->Plot(res, "r");	gr->Plot(in, "b");
	gr->Puts(mglPoint(-0.9, -1.3), "fitted:", "r:L");
	gr->PutsFit(mglPoint(0, -1.8), "y = ", "r");
	gr->Puts(mglPoint(0, 2.2), "initial: y = 0.3+sin(2\\pi x)", "b");
//	gr->SetRanges(mglPoint(-1,-1,-1),mglPoint(1,1,1));	gr->SetOrigin(0,0,0);
}