Help needed about numerical integration in matlab
in [Matlab]
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From: Muhammad on 27 Jul 2010 09:02 Hi everyone, I am trying to integrate the following function from 0 to infinity numerically in matlab: f(x)= (x/(2*l*s))^0.5*(l-1) * (exp(-0.5*(x+2*l*s))) * besseli(l , sqrt(2*l*s*x)) * ... gammainc(x , l)^(N-1); My Matlab code is: %%%%%%%%%%%%%%%%%%%%%%%%%%%%%% N = 20 ; K = 30; l = round(K/N); s = 30 ; b = 1e6; f = (x/(2*l*s))^0.5*(l-1) * (exp(-0.5*(x+2*l*s))) * besseli(l , sqrt(2*l*s*x)) * ... gammainc(x , l)^(N-1); pd = 0.5 * int(f,x,b,inf); %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% But matlab gives following error while defining function f: ??? Undefined function or method 'lt' for input arguments of type 'sym'. Error in ==> gammainc at 77 k = find(a ~= 0 & x ~= 0 & x < a+1); Error in ==> reference_strat_roc at 21 f = (x/(2*l*s))^0.5*(l-1) * (exp(-0.5*(x+2*l*s))) * besseli(l , sqrt(2*l*s*x)) * gammainc(x , l)^(N-1); How can I avoid this error or any other method to integrate this integral numerically??? Thanks TAHIR
From: us on 27 Jul 2010 09:06 On Jul 27, 3:02 pm, "Muhammad " <mtornad...(a)hotmail.com> wrote: > Hi everyone, > I am trying to integrate the following function from 0 to infinity numerically in matlab: > > f(x)= (x/(2*l*s))^0.5*(l-1) * (exp(-0.5*(x+2*l*s))) * besseli(l , sqrt(2*l*s*x)) * ... > gammainc(x , l)^(N-1); > My Matlab code is: > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%% > N = 20 ; > K = 30; > l = round(K/N); > s = 30 ; > b = 1e6; > f = (x/(2*l*s))^0.5*(l-1) * (exp(-0.5*(x+2*l*s))) * besseli(l , sqrt(2*l*s*x)) * ... > gammainc(x , l)^(N-1); > pd = 0.5 * int(f,x,b,inf); > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% > > But matlab gives following error while defining function f: > > ??? Undefined function or method 'lt' for input arguments of type 'sym'. > Error in ==> gammainc at 77 > k = find(a ~= 0 & x ~= 0 & x < a+1); > Error in ==> reference_strat_roc at 21 > f = (x/(2*l*s))^0.5*(l-1) * (exp(-0.5*(x+2*l*s))) * besseli(l , sqrt(2*l*s*x)) * gammainc(x , l)^(N-1); > > How can I avoid this error or any other method to integrate this integral numerically??? > > Thanks > > TAHIR you don't show how X is defined... the code works fine if(f) X is a DOUBLE... however, accoding to the error message, it seems to be a symbolic object... us
From: Muhammad on 27 Jul 2010 09:13 us <us(a)neurol.unizh.ch> wrote in message <79aac37d-9b9b-435f-8827-ecac84a0d5d8(a)t35g2000vbb.googlegroups.com>... > On Jul 27, 3:02 pm, "Muhammad " <mtornad...(a)hotmail.com> wrote: > > Hi everyone, > > I am trying to integrate the following function from 0 to infinity numerically in matlab: > > > > f(x)= (x/(2*l*s))^0.5*(l-1) * (exp(-0.5*(x+2*l*s))) * besseli(l , sqrt(2*l*s*x)) * ... > > gammainc(x , l)^(N-1); > > My Matlab code is: > > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%% > > N = 20 ; > > K = 30; > > l = round(K/N); > > s = 30 ; > > b = 1e6; > > f = (x/(2*l*s))^0.5*(l-1) * (exp(-0.5*(x+2*l*s))) * besseli(l , sqrt(2*l*s*x)) * ... > > gammainc(x , l)^(N-1); > > pd = 0.5 * int(f,x,b,inf); > > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% > > > > But matlab gives following error while defining function f: > > > > ??? Undefined function or method 'lt' for input arguments of type 'sym'. > > Error in ==> gammainc at 77 > > k = find(a ~= 0 & x ~= 0 & x < a+1); > > Error in ==> reference_strat_roc at 21 > > f = (x/(2*l*s))^0.5*(l-1) * (exp(-0.5*(x+2*l*s))) * besseli(l , sqrt(2*l*s*x)) * gammainc(x , l)^(N-1); > > > > How can I avoid this error or any other method to integrate this integral numerically??? > > > > Thanks > > > > TAHIR > > you don't show how X is defined... Sorry for my mistake. Yes you are right .... x is defined as syms x ; Please give any suggestion how to evaluate this integral ..... Thanks > the code works fine if(f) X is a DOUBLE... > however, accoding to the error message, it seems to be a symbolic > object... > > us
From: us on 27 Jul 2010 09:20 "Muhammad " > Sorry for my mistake. Yes you are right .... x is defined as > > syms x ; > > Please give any suggestion how to evaluate this integral ..... > > Thanks according to the title of your OP, you're looking for numerical integration... since INT() works on syms, you'd have to look into other ML functions, eg, help quad; % <- and its many siblings... us
From: Muhammad on 27 Jul 2010 09:34
"us " <us(a)neurol.unizh.ch> wrote in message <i2mmef$mua$1(a)fred.mathworks.com>... > "Muhammad " > > Sorry for my mistake. Yes you are right .... x is defined as > > > > syms x ; > > > > Please give any suggestion how to evaluate this integral ..... > > > > Thanks > > according to the title of your OP, you're looking for numerical integration... > since INT() works on syms, you'd have to look into other ML functions, eg, > > help quad; % <- and its many siblings... > > us Thanks for reply. But quad() and its versions work on scalar limits of integration but I have to evaluate the integral from a positive scalar to infinity. ??? |