FINDING INVERSE ERROR FUNCTION

In a previous blog at autarkaw.wordpress.com (Sep 1, 2010), we set up a nonlinear equation to find the inverse error function. In this blog, we will solve this equation by using interpolation. The problem is given at and we are solving Exercise 2 of the pdf file.

Contents

TOPIC

Finding inverse error function

SUMMARY

% Language : Matlab 2008a;
% Authors : Autar Kaw;
% Mfile available at
% http://numericalmethods.eng.usf.edu/blog/inverse_erf_interp_matlab.m;
% Last Revised : October 4 2010
% Abstract: This program shows you how to find the inverse error function
% using interpolation
clc
clear all

INTRODUCTION

disp('ABSTRACT')
disp('   This program shows you how to')
disp('   find the inverse error function')
disp(' ')
disp('AUTHOR')
disp('   Autar K Kaw of http://autarkaw.wordpress.com')
disp(' ')
disp('MFILE SOURCE')
disp(' http://numericalmethods.eng.usf.edu/blog/inverse_erf_interp_matlab.m')
disp('  ')
disp('PROBLEM STATEMENT')
disp(' http://numericalmethods.eng.usf.edu/blog/inverseerror.pdf  Exercise 2')
disp(' ')
disp('LAST REVISED')
disp('   October 4, 2010')
disp(' ')

ABSTRACT
   This program shows you how to
   find the inverse error function
 
AUTHOR
   Autar K Kaw of http://autarkaw.wordpress.com
 
MFILE SOURCE
 http://numericalmethods.eng.usf.edu/blog/inverse_erf_interp_matlab.m
  
PROBLEM STATEMENT
 http://numericalmethods.eng.usf.edu/blog/inverseerror.pdf  Exercise 2
 
LAST REVISED
   October 4, 2010
 

INPUTS

Value of error function

erfx=0.1125;
% Table of erf(x) vs x
xx=[0  0.1  0.25  0.75  1.0  1.5  2.0  5.0];
erfxx=[0  0.1125  0.2763  0.7112  0.8427  0.9661  0.9953  1.0000];

DISPLAYING INPUTS

disp('INPUTS')
fprintf(' Inverse error function is to be found for= %g',erfx)
disp('  ')
disp(' Given erf(x) vs x values')
disp('_______________________')
disp('    x          erfx  ')
disp('________________________')
dataval=[xx;erfxx]';
disp(dataval)

INPUTS
 Inverse error function is to be found for= 0.1125  
 Given erf(x) vs x values
_______________________
    x          erfx  
________________________
         0         0
    0.1000    0.1125
    0.2500    0.2763
    0.7500    0.7112
    1.0000    0.8427
    1.5000    0.9661
    2.0000    0.9953
    5.0000    1.0000

CODE

if erfx>1.0 | erfx<0
    disp('Invalid value. erf(x) only takes values in [0,1] range')
else

inverse_erf=interp1(erfxx,xx,erfx,'cubic');

DISPLAYING OUTPUTS

disp('OUTPUTS')
fprintf(' Value of inverse error func from this mfile is= %g',inverse_erf)
fprintf(' \n Value of inverse error func from MATLAB is    = %g',erfinv(erfx))
disp('  ')

OUTPUTS
 Value of inverse error func from this mfile is= 0.1 
 Value of inverse error func from MATLAB is    = 0.100033  

end

Published with MATLAB® 7.10