Table of Contents
1 fit-gnuplot
syntax
>> fit [xrange][yrange] function 'datafile' using modifier via paprameterfile
example:
input: house_price.dat
### 'house_price.dat' ## X-Axis: House price (in $1000) - Y-Axis: Square meters (m^2) 245 426.72 312 601.68 279 518.16 308 571.5 199 335.28 219 472.44 405 716.28 324 546.76 319 534.34 255 518.16
gnuplot> # m, q will be our fitting parameters
gnuplot> f(x) = m*x + q
gnuplot> fit f(x) 'house_price.dat' using 1:2 via m, q
iter chisq delta/lim lambda m q
0 5.8376960560e+05 0.00e+00 2.07e+02 1.000000e+00 1.000000e+00
1 1.6488461223e+04 -3.44e+06 2.07e+01 1.777346e+00 1.003262e+00
2 1.5195558950e+04 -8.51e+03 2.07e+00 1.815976e+00 1.068562e+00
3 1.4876544660e+04 -2.14e+03 2.07e-01 1.795915e+00 7.050054e+00
4 1.3188280257e+04 -1.28e+04 2.07e-02 1.594141e+00 6.715403e+01
5 1.3171060201e+04 -1.31e+02 2.07e-03 1.571627e+00 7.386063e+01
6 1.3171060179e+04 -1.63e-04 2.07e-04 1.571602e+00 7.386812e+01
iter chisq delta/lim lambda m q
After 6 iterations the fit converged.
final sum of squares of residuals : 13171.1
rel. change during last iteration : -1.62785e-09
degrees of freedom (FIT_NDF) : 8
rms of residuals (FIT_STDFIT) = sqrt(WSSR/ndf) : 40.5756
variance of residuals (reduced chisquare) = WSSR/ndf : 1646.38
Final set of parameters Asymptotic Standard Error
======================= ==========================
m = 1.5716 +/- 0.2247 (14.3%)
q = 73.8681 +/- 65.65 (88.87%)
correlation matrix of the fit parameters:
m q
m 1.000
q -0.981 1.000
To save m, and q values in a string and plotting
set terminal postscript eps font 24
set out 'house_price_fit.eps'
mq_value = sprintf("Parameters values\nm = %f k$/m^2\nq = %f k$", m, q)
# \n -->> next line
set title 'Linear Regression Example Scatterplot'
set ylabel 'House price (k$ = $1000)'
set xlabel 'Square meters (m^2)'
set style line 1 ps 1.5 pt 7 lc 'red'
set style line 2 lw 1.5 lc 'blue'
set grid
set key bottom center box height 1.4
set xrange [0:450]
set yrange [0:]
set object 1 rect from 90,725 to 200, 650 fc rgb "white"
set label 1 at 100,700 mq_value
print 'house_price.dat' ls 1 title 'House price', f(x) ls 2 title 'Linear regression'
set out
figures/gnuplot/fit/house_price_fit.pdf
