The result of g and h should not contain c

g and h are unknown， A curve represent the values of c

program：

x=[0 0.25 0.50 0.70 0.80 1.00 1.3];

y=[0 5 7 9 10 11 12];

a=polyfit(x,y,3);

syms X g h t

fy=vpa(poly2sym(a,X),4)%制定v为变量。函数默认x为自变量

x1=min(x):max(x);

h1=polyval(a,x1);

c=fy;

%syms g h t [g,h]=dsolve('Dg+5*g+c*h=exp(t)','Dh-g-3*h=0','g(0)=1','h(0)=0','t')

simplify(g);

simplify(h);

ezplot(g,h,[0,1.3]);axis auto

Answer 1

[Steven Lord]

Don't pass strings into DSOLVE. If you do that, it can't substitute the value in the variable c for the c term in the string. Take a look at the examples in the documentation for DSOLVE in your installation; if you're using a sufficiently recent release, they will show you how to define symbolic functions and use those symbolic functions to define the differential equations to be solved.