Attempt to execute SCRIPT dsolve as a function:

Hello everybody.

I need to solve a system of 3 differential equations plus a not differential one.

I tried that:

syms x y z w real

S = dsolve('Dx -(((a*(x^2+Tamb^2)*(x+Tamb)*(Tamb-x)+ (b*(x^2+Tamb^2)*(x+Tamb)+c)*(y-x)+d))/e) = 0',...
           'Dy -(((a*(x^2+Tamb^2)*(x+Tamb))*(x-y)+(f*(z-y))+((Tamb-y)/g)+(h-i*(1-l*(y - T_ref))))/m) = 0',...
           'Dz -((f*(y-z)-n*(w-Tf0))/o)=0',...
           'Dw - 2*z+Tf0 = 0',...
           'x(0)=Tamb', 'y(0)=299', 'z(0)=288','w(0)=1',...
           'IgnoreAnalyticConstraints', 'none');

but it tells me:

??? Attempt to execute SCRIPT dsolve as a function:
C:\Users\.........\dsolve.m

Error in ==> dsolve at 25
S = dsolve('Dx -(((a*(x^2+Tamb^2)*(x+Tamb)*(Tamb-x)+
(b*(x^2+Tamb^2)*(x+Tamb)+c)*(y-x)+d))/e) = 0',...

Where is the error?

Thank you very very much

[Valentina]

It gave me this error:

??? Error using ==> mupadmex

Error in MuPAD command: Illegal equations [ode::new]

Error in ==> sym.sym>sym.mupadmexnout at 2018

out = mupadmex(fcn,args{:});

Error in ==> dsolve>mupadDsolve at 190

[var_list,R] = mupadmexnout('symobj::dsolve',sys,x,ignoreConstraints);

Error in ==> dsolve at 97

[R,vars] = mupadDsolve(ignoreConstraints,varargin{1:narg});

Error in ==> RisolutoreMySYST at 130

S = dsolve('Dx - (((a*(x^2+Tamb^2)*(Tamb-x)+ b*(((0.0552*Tamb^1.5)^4)-x^4) +

b*(Tamb^4-x^4)+ c*(y-x) + d))/e) = 0',...

What's that?

Answer 1

[Walter Roberson]

You named your own file dsolve and that is interfering with calling the MATLAB dsolve

[Valentina]

Thank you. Now it works (but it doesn't find an explicit solution -nor an implicit one- and it returns me empty syms).

[berkeley]

Hi，Walter

I try to solve Dx=Ax； while x is of 2*1 elements,

 A=[2 1;3 2];f=dsolve('Dx=A*x','x(0) = [32 20]');

Warning: Explicit solution could not be found. > In dsolve at 101

Not so surprising, no Explicit solution ,at leaast no errors.

But when I change x to 3*1 elements, it comes the following errors, so amazing!!!

Thanks for your help

A=[1 2 1;1 5 6;4 2 1]; f=dsolve('Dx=A*x','x(0) = [20;20;20]');

??? Error using ==> mupadmex

Error in muPAD command: Illegal equations [ode::new]

Error in ==> sym.sym>sym.mupadmexnout at 2003 out = mupadmex(fcn,args{:});

Error in ==> dsolve>mupadDsolve at 190 [var_list,R] = mupadmexnout('mllib::dsolve',sys,x,ignoreConstraints);

Error in ==> dsolve at 97 [R,vars] = mupadDsolve(ignoreConstraints,varargin{1:narg});

[Walter Roberson]

Please start a new Question for this.