I am complete new , and do not know how to modify this~

   syms x
      T=1;
  lamda=0.5;
  gamma=1;
  t=0.1;
  theta=0.1;
  U=lamda/(0.5*theta^2+lamda);
  V0(x)=-U.*exp(-gamma.*x)+(1-U).*exp(-(0.5.*theta.^2+lamda).*(T-t)).*exp(-gamma.*x);
      R=-diff(V0)./diff(V0,2)

Error:
The following error occurred converting from sym to double:
Error using mupadmex
Error in MuPAD command: DOUBLE cannot convert the input expression into a double array.

If the input expression contains a symbolic variable, use the VPA function instead.

Answer 1

[Walter Roberson]

You have

    V0(x)=-U.*exp(-gamma.*x)+(1-U).*exp(-(0.5.*theta.^2+lamda).*(T-t)).*exp(-gamma.*x);

which attempts to index something at the symbolic variable x. Your MATLAB is attempting to convert that symbolic x into a numeric value to use as an index in to V0.

You need to add

syms V0(x)

before you have that statement so that MATLAB knows you are defining a symbolic function.

If MATLAB complains about

syms V0(x)

being a syntax error then you have a version of MATLAB that is too old to support that. If that happens then instead use

V0 = -U.*exp(-gamma.*x)+(1-U).*exp(-(0.5.*theta.^2+lamda).*(T-t)).*exp(-gamma.*x);
R = -diff(V0,x) ./ diff(V0,x,2);

[Shican Liu]

Yeah, that is right, my matlab is an old version, but it's already done, 3Q very much~~