problem using variables solving trigonometric equation with "solve('...')

Hi all,

I am trying to solve a trigonometric equation. It works just fine if I put a number in the solver, but return an error if I type a variable.

For example:

syms x;
solve('sin(x) = x -1')

works perfectly.

However, when I try:

syms x;
a = 1;
solve('sin(x) = x -a')

I get the error:

Warning: Explicit solution could not be found. 
> In solve at 81
ans =
[ empty sym ]

As the equation in integrated in some code, it is of no use if I cannot solve it with the variable. If someone has an idea it would be great!

Cheers, Flavien

Answer 1

[Aaditya Kalsi]

It may be better to define 'a' as a symbolic variable and not a double.

 syms x;
 a = sym('1');
 f = sin(x) -x + a;
 myVal = solve(f, x);

[Walter Roberson]

Defining it as a symbolic variable doesn't matter.

a = 1

f = sin(x) - x + a;

myVal = solve(f,x);

Answer 2

[Walter Roberson]

syms x;
a = 1;
solve(subs(sym('sin(x) = x -a')));

The MATLAB-level value of a variable is not used within a quoted string (such as you were solving for) unless you use the subs() operation to request the substitution.