Update eigen.rst

Author: mhscott

source/user/manual/analysis/eigen.rst

@@ -5,14 +5,15 @@ eigen Command
 
 This command is used to perform the eigenvalue analysis.
 
-.. function:: eigen <$solver> $numEigenvalues
+.. function:: eigen <type> <$solver> $numEigenvalues
 
 .. csv-table:: 
    :header: "Argument", "Type", "Description"
    :widths: 10, 10, 40
 
    $numEigenvalues, |integer|, number of eigenvalues required.
-   $solver, |string|, "optional string detailing type of solver: -genBandArpack, -symmBandLapack, -fullGenLapack (default: -genBandArpack)."
+   $solver, |string|, "optional string detailing type of solver: -genBandArpack (default), -fullGenLapack, -symmBandLapack."
+   $type, |string|, optional string indicating type of eigenvalue problem to solve: 'general' (default) or 'standard'
 
 .. admonition:: Returns
 
@@ -22,6 +23,7 @@ This command is used to perform the eigenvalue analysis.
 .. note::
    1.  The eigenvectors are stored at the nodes and can be printed out using a Node Recorder, the nodeEigenvector command, or the Print command.
    2.  The default eigensolver is able to solve only for N-1 eigenvalues, where N is the number of inertial DOFs. When running into this limitation the -fullGenLapack solver can be used instead of the default Arpack solver.
+   3. The -symmBandLapack option works only standard eigenvalue analysis of the stiffness matrix, i.e., K*x = lam*x
 
 Theory
 ^^^^^^
@@ -51,6 +53,9 @@ Theory
       # or, obtain 10 eigenvalues explicitly specifying the solver
       set eigenvalues [eigen -fullGenLapack 10]
 
+      # obtain 10 eigenvalues of the stiffness matrix
+      set eigenvalues [eigen standard -symmBandLapack 10]
+
    2. **Python Code**
 
    .. code:: python
@@ -61,4 +66,7 @@ Theory
       # or, obtain 10 eigenvalues explicitly specifying the solver
       eigenvalues = eigen('-fullGenLapack', 10)
 
+      # obtain 10 eigenvalues of the stiffness matrix
+      eigenvalues = eigen('standard','-symmBandLapack',10)
+
 Code Developed by: |fmk|