restore,'circdata.sav'
ploterror,x,y,xerr,yerr,ps=1

guessp = [30., 50., 10., (3./!radeg), (32./!radeg)]

fa = {T:t, XVAL:x, YVAL:y, XERR:xerr, YERR:yerr}

p = mpfit('mycirc',guessp,functargs=fa)

plot_t = findgen(100)
outx = p[0] + p[2]*sin(p[3]*plot_t + p[4])
outy = p[1] + p[2]*cos(p[3]*plot_t + p[4])

oplot,outx,outy,color=getcolor('red'),thick=3

stop

end