Hi everyone, I'm having problem trying to solve for the integral of the cumulative distribution function for my thesis. I want to hold x as variable for F(x) and solve it later to optimize it. The problem is the function normcdf(x,mu,sigma) doesn't allow me to define x as symbol, it require x to be a double value instead. So my question is, is there anyway to define x as "syms x" and then use normcdf(x,mu,sigma)?
With the uniform distribution I write the function straightforward in the program like this:
gamma = 0; n = 150; syms e Q_sc Q_r X Pi_sc Pi_r S_Q S_Q2 x h t; S_Q = Q_sc - int(((e-gamma+n)/(2*n)),e,0,Q_sc - D_r); S_Q2 = Q_r - int(((e-gamma+n)/(2*n)),e,0,Q_r - D_r); Pi_sc = (S_Q*(p-c_m-s+g_r+g_m+(G1*(s_return-l_m-l_r-r)))) + ((s-c_r)*Q_sc) - ((g_r+g_m)*D_r); Diff_Pi_sc = diff(Pi_sc,'Q_sc'); Q_sc = solve(Diff_Pi_sc); Q_sc = vpa(Q_sc);
So instead of writing unifcdf(...), I use ((e-gamma+n)/(2*n)) instead, because I want to keep "e" as variable, I don't want the program to calculate in right away. Is there anyway I can achieve this task using unifcdf function provided by the program?
Thank you very much in advance
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If you need to use Symbolic Toolbox sym variables, then you may want to use the erfc function in place of normcdf. Consider this:
>> mu = 10; sigma = 2; >> normcdf(10:13,mu,sigma) ans = 0.5000 0.6915 0.8413 0.9332
Here's how to get to get that answer using a sym:
>> syms x >> y = .5*erfc(-(x-mu)/(sigma*sqrt(2))); >> subs(y,x,10:13) ans = [ 1/2, 1 - erfc(2^(1/2)/4)/2, 1 - erfc(2^(1/2)/2)/2, 1 - erfc((3*2^(1/2))/4)/2] >> double(ans) ans = 0.5000 0.6915 0.8413 0.9332
Dear Tom Lane, I want to integrate a cdf function, however getting error "??? Undefined function or method 'erfc' for input arguments of type 'sym'." The Matlab code is given below.Please suggest me what to do? sym x f1(i) =int(normcdf(x,mu,sigma),0,1000); f2(i) =int(normcdf(x,mu,sigma),1600,2000); G(i) = double(f1(i)+f2(i));