Exponential Integral
in [Matlab]
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From: sitiroy Roy on 12 Aug 2010 14:18 Hi, I am trying to integrate a generalized exponential integral E_nu(z) where my nu=0.7 and z=-0.5 Can I do it in MATLAB? or is there any package by which I can do it? roy
From: Roger Stafford on 12 Aug 2010 15:43 "sitiroy Roy" <sitiroy(a)gmail.com> wrote in message <i41dst$2st$1(a)fred.mathworks.com>... > Hi, > > I am trying to integrate a generalized exponential integral E_nu(z) > where my nu=0.7 and z=-0.5 > > Can I do it in MATLAB? > > or is there any package by which I can do it? > > roy - - - - - - - - - I believe E_p(x) can be evaluated in terms of the incomplete gamma function and matlab has that function for real values of x. E_p(x) = int(exp('-x*t)/t^p','t',1,inf) = x^(p-1)*int('exp(-s)/s^p','s',x,inf) where the substitution s = x*t is made. This latter integral can be found from matlab's gammainc with the 'upper' option. (Remember, though, that gammainc is normalized.) It wasn't clear whether you wanted to evaluate E_nu(z) or integrate it. Your use of the letter z suggests you want it with complex values, but the value -0.5 you assigned it is real. I believe matlab's incomplete gamma function can only use real arguments. Roger Stafford
From: sitiroy Roy on 12 Aug 2010 15:59 Hi Roger, I tried that already, but MATLAB is giving me that in gammainc(1-nu, A), A should be real and non-negative. A=-0.5 is real but negative, so the ERROR I just needed to evaluate it. I had a anaother function, whose integral is given in terms of the exponential intergarl. thanks FOR THE RESPONSE ROY Roger Stafford" <ellieandrogerxyzzy(a)mindspring.com.invalid> wrote in message <i41isa$ksb$1(a)fred.mathworks.com>... > "sitiroy Roy" <sitiroy(a)gmail.com> wrote in message <i41dst$2st$1(a)fred.mathworks.com>... > > Hi, > > > > I am trying to integrate a generalized exponential integral E_nu(z) > > where my nu=0.7 and z=-0.5 > > > > Can I do it in MATLAB? > > > > or is there any package by which I can do it? > > > > roy > - - - - - - - - - > I believe E_p(x) can be evaluated in terms of the incomplete gamma function and matlab has that function for real values of x. > > E_p(x) = int(exp('-x*t)/t^p','t',1,inf) > = x^(p-1)*int('exp(-s)/s^p','s',x,inf) > > where the substitution s = x*t is made. This latter integral can be found from matlab's gammainc with the 'upper' option. (Remember, though, that gammainc is normalized.) > > It wasn't clear whether you wanted to evaluate E_nu(z) or integrate it. Your use of the letter z suggests you want it with complex values, but the value -0.5 you assigned it is real. I believe matlab's incomplete gamma function can only use real arguments. > > Roger Stafford
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