Dear all,
This seems to be a pretty simple question but I am struggling to find any help on the topic!
I have recently started using COMSOL with the livelink to write a Model Order Reduction in MATLAB. The goal is to use COMSOL to generate the system matrices and eventually solve the problem in MATLAB.
To this end, the command mphmatrix should be of great help. The help page for this function tells us that we can retrieve following system matrices:
'K' Stiffness matrix
'L' Load vector
'M' Constraint vector
'N' Constraint Jacobian
'D' Damping matrix
'E' Mass matrix
'NF' Constraint force Jacobian
'NP' Optimization constraint
Jacobian(*)
'MP' Optimization constraint vector(*)
'MLB' Lower bound constraint vector(*)
'MUB' Upper bound constraint vector(*)
'Kc' Eliminated stiffness matrix
'Lc' Eliminated load vector
'Dc' Eliminated damping matrix
'Ec' Eliminated mass matrix
'Null' Constraint null-space basis
'Nullf' Constraint force null-space
matrix
'ud' Particular solution ud
'uscale' Scale vector
Moreover with the command mphgetu, one can retrieve solution vector U and its first derivative Udot at any given time.
The problem is nowhere can I find what linear system is COMSOL solving. I can only fathom it is:
E*Udotdot + D*Udot + K*U == L
What is even more surprising is that the model has 2315 degrees of freedom (dofs) plus 6 internal dofs. Matrices E, D and K are 2315x2315, vector L is 2315x1. Very well. However U as retrieved with command mphgetu is 2321x1 ! U seems to include the 6 internal dofs.
My question is, where can I find help/documentation on what linear system COMSOL solves, and where can one find what is the correlation between U and dofs. mphxmeshinfo seems promising but the documentation for that function is vague.
Many many thanks for all help.
Best regards,
Guillaume
This seems to be a pretty simple question but I am struggling to find any help on the topic!
I have recently started using COMSOL with the livelink to write a Model Order Reduction in MATLAB. The goal is to use COMSOL to generate the system matrices and eventually solve the problem in MATLAB.
To this end, the command mphmatrix should be of great help. The help page for this function tells us that we can retrieve following system matrices:
'K' Stiffness matrix
'L' Load vector
'M' Constraint vector
'N' Constraint Jacobian
'D' Damping matrix
'E' Mass matrix
'NF' Constraint force Jacobian
'NP' Optimization constraint
Jacobian(*)
'MP' Optimization constraint vector(*)
'MLB' Lower bound constraint vector(*)
'MUB' Upper bound constraint vector(*)
'Kc' Eliminated stiffness matrix
'Lc' Eliminated load vector
'Dc' Eliminated damping matrix
'Ec' Eliminated mass matrix
'Null' Constraint null-space basis
'Nullf' Constraint force null-space
matrix
'ud' Particular solution ud
'uscale' Scale vector
Moreover with the command mphgetu, one can retrieve solution vector U and its first derivative Udot at any given time.
The problem is nowhere can I find what linear system is COMSOL solving. I can only fathom it is:
E*Udotdot + D*Udot + K*U == L
What is even more surprising is that the model has 2315 degrees of freedom (dofs) plus 6 internal dofs. Matrices E, D and K are 2315x2315, vector L is 2315x1. Very well. However U as retrieved with command mphgetu is 2321x1 ! U seems to include the 6 internal dofs.
My question is, where can I find help/documentation on what linear system COMSOL solves, and where can one find what is the correlation between U and dofs. mphxmeshinfo seems promising but the documentation for that function is vague.
Many many thanks for all help.
Best regards,
Guillaume