Second argument must be a scalar or vector of unique symbolic variables.

I was using dsolve to solve a differential equation. The code is:

clear all; close all; clc;
syms X;
syms gamma;
syms Y;
syms p(t);
ode = diff(p,t) == X * p ^ (3/2 - 1 / (2 * gamma)) - Y * diff(p,t);
ysol(t) = dsolve(ode);

but I got the error:

Error using symfun.validateArgNames (line 122)

Second argument must be a scalar or vector of unique symbolic variables.

Error in symfun (line 144)

y.vars = symfun.validateArgNames(inputs);

Error in symfun/privResolveArgs (line 291)

argout{k} = symfun(argout{k},fvars);

Error in sym/privBinaryOp (line 1072)

args = privResolveArgs(A, B);

Error in ^ (line 382)

B = privBinaryOp(A, p, 'symobj::mpower');

Error in differential_function (line 8)

ode = diff(p,t) == X * p ^ (3/2 - 1 / (2 * gamma)) - Y * diff(p,t);

So, could anyone tell me what is wrong?

And after I restrated MATLAB and reran the code, I got different errors, like:

Error using mupadengine/feval2sym_NaNsingularity

No differential equations found. Specify differential equations by using symbolic functions.

Error in dsolve>mupadDsolve (line 334)

T = feval2sym_NaNsingularity(symengine,'symobj::dsolve',sys,x,options);

Error in dsolve (line 203)

sol = mupadDsolve(args, options);

Error in differential_function (line 10)

ysol(t) = dsolve(ode);

Related documentation

Maybe somthing wrong with my PC?

And I use MATLAB online, I got

Also, actually the equation was solved at first and I did not change a thing, where the answer is

So, why suddenly it failed and why there is a zero in the second line of the solution?

Answer 1

[Paul]

No error if running here w/2024b, nor did I get an error running on my local machine with 2024a

syms X;
syms gamma;
syms Y;
syms p(t);
ode = diff(p,t) == X * p ^ (3/2 - 1 / (2 * gamma)) - Y * diff(p,t)
ysol(t) = dsolve(ode)

p(t) = 0 is a trivial solution to the differenial equation, but I'm not sure why it's being returned. As far as I know, the trivial solution is typically not returned.

disp(char(ysol))

[((1/(2*gamma) - 1/2)*(C1 + (X*t)/(Y + 1)))^(1/(1/(2*gamma) - 1/2)); 0]

Note: symbolic rendering still not working after submitting @Tushal Desai

[奥 刘]

Really thanks for the answer. So maybe something wrong with my PC I guess.

[Paul]

Mabye you have symbolic diff shadowed? Does ode look like what you expect? What do you see from the command

which diff(p,t)

if executed before the call to dsolve

[奥 刘]

Sorry for the late reply. For

which diff(p,t)

I got

D:\software\Code thing\Matlab2024a\toolbox\symbolic\symbolic\@sym\diff.m % symfun method

What do you mean by symbolic diff shadowed? Sorry I am not familiar with this area.

[Walter Roberson]

The problem is not with diff() -- if it were then it would have complained about diff() since diff() is earlier in the expression.

The problem it is complaining about is

Error in ^ (line 382)

refering to

ode = diff(p,t) == X * p ^ (3/2 - 1 / (2 * gamma)) - Y * diff(p,t);

the ^ is between the p and the (3/2 - 1 / (2 * gamma))

[奥 刘]

@Walter Roberson Yes! That's the problem. Really thanks Walter!