How can I calc eigenvalues to fourier series?

Sometimes you've got to calculate eigenvalues to solve fourier series. I don't know how to calc in matlab. For example, to an eigenvalue lambda and a,b e d are constants.

a*d/lambda*sin(lambda/d)+b*cos(lambda/d)=0

Thank you

[Walter Roberson]

Please clarify what your input is. If it is a matrix, then eig() can be used to solve the eigenvalues.

[Marco Esteves]

my inputs are the constants a,b and d with a*b>0.

my output is lambda,the eigenvalue. But lambda is an array, indexed at discrete time,so can be called lambda_n with n=1:infinity

[Walter Roberson]

None of your inputs are time-dependent. I did some quick testing, and found that often there is only one solution. Even if there are multiple solutions, what ordering would you impose on them to allow them to be indexed ?