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conversion frm sym to double is not possible?

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khushi
khushi 2015-8-22
评论： Walter Roberson 2015-8-22
clc;
clear all;
g_db=[0:1:40];
g=10.^(g_db/10);
c=1;
syms y
%g=0:0.1:10;
alpha=1;
p=0.5*((g)+exp(-g.*y));
q=((y.^(alpha-1)).*exp(-y./c))/((gamma(alpha))*(c^alpha));
r=p*q;
semilogy(g_db,r,'o')
hold on

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回答（1 个）

Walter Roberson
Walter Roberson 2015-8-22
Your y is a symbol. p uses y so p is symbolic. q uses y so q is symbolic. Two symbolic values multiplied together is going to be symbolic. Therefore r is symbolic.
You then try to semilogy() with the second argument being that symbolic r. semilogy is not able to plot symbolic results.
In order to plot something that is in symbolic form, all of the symbolic variables in the expression must be given specific numeric values. For example,
semilogy(g_db, double(subs(r,y,linspace(0,1,20)), 'o')

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