Support Knowledge Base

Error: Singular Matrix

Solution Number: 953 Versions: All versions

What does the error message "Singular Matrix" mean? The problem is that the stiffness matrix of the linear system is singular and the linear solver cannot invert it. Examples of practical modeling situations where this ...

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Avoiding negative concentrations

Solution Number: 952 Applies to: COMSOL Multiphysics, CFD Module, Chemical Reaction Engineering Module, Electrodeposition Module, Microfluidics Module, Subsurface Flow Module, Mixer Module, Corrosion Module, Electrochemistry Module Versions: All versions

Why do I get negative values of the concentration in my diffusion, convection and reaction model? Why do I see values that go below, or above, their lowest, or highest, possible values based upon the boundary ...

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Troubleshooting graphics issues

Solution Number: 933 Versions: All versions

Chances are that there is a graphics rendering problem if any of these symptoms show up: The graphics window is black It is not possible to mouse-select objects in the graphics window The COMSOL application crashes ...

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Computing Time and Space Integrals

Solution Number: 913 Versions: All versions

How do I compute integrals over space or time? What if I want to use the result of these integrals elsewhere in my model? The COMSOL Multiphysics architecture allows you to evaluate integrals in both space and time in ...

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How does COMSOL Multiphysics handle complex-valued numbers and problems in the frequency domain?

Solution Number: 878 Applies to: AC/DC Module, Acoustics Module, COMSOL Multiphysics, MEMS Module, Plasma Module, RF Module, Semiconductor Module, Structural Mechanics Module, Wave Optics Module Versions: All versions

How does COMSOL Multiphysics handle complex-valued numbers and problems in the frequency domain? Should I use the RMS, the peak, or the instantaneous value to specify sources in models being solved in the frequency ...

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What does degrees of freedom (DOFs) mean in COMSOL Multiphysics?

Solution Number: 875 Versions: All versions

What does degrees of freedom (DOFs) mean in COMSOL Multiphysics? The solution time and memory requirements are strongly related to the number of degrees of freedom in the model. It is often desirable to be able to ...

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How do I solve a PDE with space derivatives of order higher than two?

Solution Number: 816 Versions: All versions

How do I solve a PDE with space derivatives of order higher than two? For example, the equation for a function . Introduce names for the second derivatives of u, say . Then the equation can be written . ...

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Handling large models

Solution Number: 830 Versions: All versions

Models with many domains, boundaries, and physics features are slow to work with. Large models can contain hundreds or even thousands of domains, boundaries, and physics features. Such a large number of features ...

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Modeling of step transitions

Solution Number: 905 Versions: All versions

You may want to define loads, material properties, or boundary conditions that vary abruptly with respect to the solution, or with respect to time. This can, however, lead to a solution which is discontinuous in space ...

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Could not obtain license for COMSOL Multiphysics GUI

Solution Number: 903 Versions: All versions

Any of the following errors can appear for example if the COMSOL application has problems communicating with the license manager: License error: -15. Cannot connect to license server system. License error: -96. ...

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