Rank: 619 based on 113 downloads (last 30 days) and 7 files submitted
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Per Sundqvist

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Company/University
Chalmers Tekniska Högskola

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Professional Interests:
quantum and mathematical physics

 

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Files Posted by Per View all
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(last 30 days) 		Comments Rating
09 Jan 2009 Screenshot Exponential fit, without start-guess Fits 1) f=s1+s2*exp(-t/s3) or 2) f=s1+s2*exp(-t/s3)+s4*exp(-t/s5) to numerics, without startguess Author: Per Sundqvist exponential, nonlinear, initial guess, fit, exact, least square 40 10
  • 3.55556
3.6 | 10 ratings
12 Nov 2008 3D Data Interpolation 3D interpolation using modified 4-point vector Newton interpolation Author: Per Sundqvist mathematics, 3d interpolation, newton, interpolation, nonuniform, approximation 14 5
  • 2.5
2.5 | 6 ratings
16 Jan 2008 Screenshot erfi function Imaginary error function (could be complex) using matlab's incomplete gamma function gammainc Author: Per Sundqvist complex, gaussian, imaginary error funct..., integral 19 5
  • 2.33333
2.3 | 3 ratings
13 Jan 2005 Orthogonal Linear Regression Fits a line y=p0+p1*y to a dataset (xdata,ydata) in an orthogonal way. Author: Per Sundqvist approximation, interpolation, linear regression, interpolation orthogo..., least squares fit 10 11
  • 3.0
3.0 | 8 ratings
22 Nov 2004 Screenshot Points Inside polygone Finds those points (xi,yi) who are inside the polygon, defined by the vectors (x,y) Author: Per Sundqvist approximation, interpolation, 2d contour, random, find, polygon 1 3
  • 2.0
2.0 | 2 ratings
Comments and Ratings by Per
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03 Nov 2008 Exponential fit, without start-guess Fits 1) f=s1+s2*exp(-t/s3) or 2) f=s1+s2*exp(-t/s3)+s4*exp(-t/s5) to numerics, without startguess Author: Per Sundqvist

HI, B. Roossien. I'm not sure what kind of help you want. The code is standard but assumes perhaps that you are a bit familiar with matlab. nargin<4 means that your input arguments are 3 and you will then get options as specified, later on, at the end of the program used in the matlab function lsqcurvefit. Maby I should tell that t and f should be vectors of the same size? Or do you want me to explain the theoretical model? Its lengthy though...

As well I realize now that I in the beginning of the program should have wrote:
t=t(:);
f=f(:);
[t,ix]=sort(t);
f=f(ix);
%to make time and function f vectors sorted column vectors in case they have a funny formate like matrices.
/Per
Comments and Ratings on Per's Files View all
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21 Jun 2011 erfi function Imaginary error function (could be complex) using matlab's incomplete gamma function gammainc Author: Per Sundqvist OUKILA, Mohamed Yassin

what is erfz2?
19 May 2011 erfi function Imaginary error function (could be complex) using matlab's incomplete gamma function gammainc Author: Per Sundqvist Pisani, Marcelo

Function gives wrong results for high moduli input. For instance, using Maple ERF converted to DOUBLE (erfz2 function below):

>> z=3+2i; erfz2(z*i)/i, erfi(z)
ans =
   8.6873 -20.8295i
ans =
   8.6873 -20.8295i

>> z=7+7i; erfz2(z*i)/i, erfi(z)
ans =
  -0.0561 + 1.0102i
ans =
  7.3774e+024 +1.6269e+025i
13 May 2011 Exponential fit, without start-guess Fits 1) f=s1+s2*exp(-t/s3) or 2) f=s1+s2*exp(-t/s3)+s4*exp(-t/s5) to numerics, without startguess Author: Per Sundqvist Le, Tung
10 Mar 2011 Exponential fit, without start-guess Fits 1) f=s1+s2*exp(-t/s3) or 2) f=s1+s2*exp(-t/s3)+s4*exp(-t/s5) to numerics, without startguess Author: Per Sundqvist Gaszton
01 Nov 2010 erfi function Imaginary error function (could be complex) using matlab's incomplete gamma function gammainc Author: Per Sundqvist PLH

The program does not work as stated. When using complex z (i.e., not pure real, or pure imaginary), I get the following error:

Error using ==> gammainc
Inputs must be real, full, and double or single.

Error in ==> erfi at 19
ans=~isreal(x).*(-(sqrt(-x.^2)./(x+isreal(x))).*gammainc(-x.^2,1/2))+...

This also occurs for Example 2 provided with the code. I'm assuming it's a trivial problem since the figure above seems to correspond to what I would expect (look at the erfi article on Mathworld ). In case it's relevant, I'm using Matlab 7.10.0.499 (R2010a) (64-bit).

Top Tags Applied by Per
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approximation, interpolation, 2d contour, 3d interpolation, complex
Files Tagged by Per View all
  • 1 - 5 of
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Updated   File Tags Downloads
(last 30 days) 		Comments Rating
09 Jan 2009 Screenshot Exponential fit, without start-guess Fits 1) f=s1+s2*exp(-t/s3) or 2) f=s1+s2*exp(-t/s3)+s4*exp(-t/s5) to numerics, without startguess Author: Per Sundqvist exponential, nonlinear, initial guess, fit, exact, least square 40 10
  • 3.55556
3.6 | 10 ratings
12 Nov 2008 3D Data Interpolation 3D interpolation using modified 4-point vector Newton interpolation Author: Per Sundqvist mathematics, 3d interpolation, newton, interpolation, nonuniform, approximation 14 5
  • 2.5
2.5 | 6 ratings
16 Jan 2008 Screenshot erfi function Imaginary error function (could be complex) using matlab's incomplete gamma function gammainc Author: Per Sundqvist complex, gaussian, imaginary error funct..., integral 19 5
  • 2.33333
2.3 | 3 ratings
13 Jan 2005 Orthogonal Linear Regression Fits a line y=p0+p1*y to a dataset (xdata,ydata) in an orthogonal way. Author: Per Sundqvist approximation, interpolation, linear regression, interpolation orthogo..., least squares fit 10 11
  • 3.0
3.0 | 8 ratings
22 Nov 2004 Screenshot Points Inside polygone Finds those points (xi,yi) who are inside the polygon, defined by the vectors (x,y) Author: Per Sundqvist approximation, interpolation, 2d contour, random, find, polygon 1 3
  • 2.0
2.0 | 2 ratings

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