Solve function:Error using sym/solve>getEqns

I am having a trouble using the solve function to solve for B

syms B 
M= 1024;
solve('1e-6 = (4/log2(M))*qfunc(sqrt(3*B*log2(M)/(M-1)))',B)

I am getting these now

Error using sym/solve>getEqns

List of equations must not be empty.

Error in sym/solve (line 226)

[eqns,vars,options] = getEqns(varargin{:});

Error in untitled (line 65)

solve('1e-6 = (4/log2(M))*qfunc(sqrt(3*B*log2(M)/(M-1)))',B)

Answer 1

[Torsten]

"qfunc" does not accept symbolic input, and your B is symbolic.

Answer 2

[Star Strider]

Looking at the documentation for qfunc it is straightforward to create a symbolic version —

syms B symqfunc(x) 
M= 1024;
symqfunc(x) = erfc(x/sqrt(2)) / 2;
Eqn = 1e-6 == (4/log2(M))*symqfunc(sqrt(3*B*log2(M)/(M-1)));
solve(Eqn,B)

Warning: Unable to solve symbolically. Returning a numeric solution using vpasolve.

ans = 

710.5514874680311536574153363861

.

[Abdelaziz Gohar]

Thank you!

[Star Strider]

My pleasure!

[Esteban Patricio Tipan Mantilla]

could you explain this line pls

symqfunc(x) = erfc(x/sqrt(2)) / 2;

[Star Strider]

@Esteban Patricio Tipan Mantilla —

Quoting Torsten’s comment:

"qfunc" does not accept symbolic input, and your B is symbolic.

It creates a symbolic version of qfunc.

[Esteban Patricio Tipan Mantilla]

Thank you!