Version 4.0 introduces many new ideas and concepts to make it easier for you to create models. The following are the most important updates to the graphical user interface:
New Layout:
In version 4.0 it is easier to organize and design models with the intuitive structure of the COMSOL Desktop. The Model Builder displays all the features of your model in one place.
Personalized desktop:
Control how you organize the COMSOL Desktop layout—your preferences are saved for the next time you open COMSOL Multiphysics.
Sequences of operations:
You can now build custom model sequences to generate your geometry, physics, mesh, studies, and results. The sequences can be edited and changes are automatically updated across the model. Operations in the sequences can be modified by the parametric solver.
Geometric parametric sweeps:
With geometry sequences COMSOL can perform geometric parameter sweeps with full associativity from the user interface.
Material settings:
Materials are now administrated in one node in the Model Builder. You can select a material and its properties for each domain and for all physics in that domain..
Multiple solutions and meshes:
With the new layout, you can save and view multiple solutions and meshes, and compare and contrast the results in the Results branch.
Probes:
Use probes to visualize scalar quantities during computations. The quantities can be defined as integrals, max/min, the average of a field quantity, or the value at a point. This now works for time stepping and parameter sweeps.
Dynamic help:
The new contextdependent help enables easy browsing with extended search functionality. The Help Desk provides access to the complete documentation set.
Improved graphics:
Faster, better looking graphics.
Model settings:
Access to the model settings is easier and more intuitive. When you select a node in the Model Builder, a docked window containing associated settings displays at the same time.
Predefined selections:
Define selections of domains, boundaries, edges, and points. These predefined selections are available in the Settings windows for the physics interfaces, meshing, and when studying the results.
LiveLink family of products for integrating with CAD and MATLAB
The new LiveLink™ for SolidWorks®, LiveLink for Inventor®, and LiveLink for SolidWorks® products connect COMSOL Multiphysics directly with these CAD programs for interactively linking parameters specified in a CAD system with simulation geometry. In addition, LiveLink for MATLAB® is available for incorporating COMSOL Multiphysics models in the MATLAB technical computing and programming environment.
Cluster support
A floating network license for COMSOL Multiphysics can be extended at no additional cost to computational nodes for clusters on the Windows Cluster Server 2003, Windows HPC Server 2008, and Linux platforms.
COMSOL version 4 also introduces:
 New and enhanced physics interfaces and predefined multiphysics interfaces

New parallel solvers and higher solver performance:
 A modal solver for frequency response and time domain (for structural and acoustics simulations, for example)
 The MUMPS and SPOOLES direct solvers for parallel and cluster computing
 A time discrete solver
 A fastfrequency sweep solver using AWE (asymptotic waveform evaluation) for electromagnetic waves simulations, for example
Backward Compatibility
All backward compatibility issues are planned to be solved for version 4.0a unless explicitly stated.
Deformed Geometry Interface
The Parameterized Geometry application mode in versions 3.5a, which is limited to 2D, is replaced with the Deformed Geometry interface in version 4.0. This interface is available in 2D and 3D. The Deformed Geometry interface deforms the mesh using an arbitrary LagrangianEulerian (ALE) method and is not the parameterized geometry using geometric parameter sweeps (see above), which is new functionality in version 4.0.
In the version 4.0 interface, the Linear Displacement and Similarity Transform boundary conditions are not yet available as preset conditions.
In order to compensate, you can create the corresponding conditions by manually entering variables that reflect such conditions in version 4.0.
Identity Couplings
A COMSOL V4 file can contain several model nodes in the Model Builder. This corresponds to using several geometries in version 3.5a. The functionality makes it possible to study a system consisting of several components, which can be described in the same dimension or in different dimensions (3D, 2D, 1D).
In version 4.0, the identity coupling between different model nodes is not yet implemented.
If you have a model with several geometries in version 3.5a and have used identity couplings between these different geometries, you have to manually replace the identity coupling with an extrusion coupling to connect the corresponding model nodes in version 4.0.
Max/Min Markers
Max/min markers in version 3.5a show the position and value of the maximum and minimum point of a field in a domain during postprocessing.
These max/min markers are not yet available in Results in version 4.0.
Moving Mesh Interface
Weak constraints are typically required when you need to set both displacement and displacement velocity as a boundary condition on a single boundary in the Moving Mesh interface. Such instances are unusual, though.
Weak constraints are not yet available in the Moving Mesh interface in version 4.0.
Pairs Boundary Conditions
Pairs are used to connect boundaries between domains that are separated by an assembly boundary (boundary between different parts in an assembly). To create an assembly, you have to either import it from a CAD package or actively form an assembly as a final step in the COMSOL geometry sequence.
Pair boundary conditions are available as general conditions for all application modes in versions 3.5a. In version 4.0, the pair boundary conditions are defined by each physics interface. This has the advantage that they can be named and tailored for the different physics at hand.
However, there may be cases where a model implemented in version 3.5a lacks the corresponding pair boundary condition in version 4.0. There are workarounds but these depend on the type of boundary condition. Please contact technical support if you have a model that requires this.
Periodic Pair Boundary Conditions
Periodic boundary conditions are used to model repetitive structures, where one boundary in a domain is identical to another boundary in the same domain.
Periodic boundary conditions are available as general conditions for all application modes in version 3.5a. In version 4.0, this functionality is a tailored condition for each physics interface.
However, some physics interfaces may lack periodic boundary conditions in version 4.0; see the Backwards Compatibility section for the modules below.
Note that all physics interfaces will include periodic boundary conditions in the future.
PDE Modes
Basis Functions or Elements
The PDE application mode in version 3.5a includes a number of possible basis functions or elements to be used in the finite element formulation of a set of equations.
Only Lagrange basis elements are available in the PDE interfaces in version 4.0 using the General form or Coefficient form. Discontinuous elements are available by entering expressions as weak contributions using auxiliary dependent variables.
Other elements are not yet available in the PDE interfaces.
Generalized Neumann Boundary Condition
The q coefficient in version 3.5a can be used to directly specify a flux perpendicular to a boundary as a linear function of the dependent variables.
The q coefficient is not available as a readymade setting in version 4.0.
In version 4.0, the replacement action is to manually specify a flux perpendicular to a boundary as a linear function of the dependent variable by combining the expressions for the q coefficient with the dependent variable. For example, you can use g = {−q11u1 ,−q12u2; −q21u1, −q22u2} for the case of two dependent variables, u1 and u2.
Units
The SI unit base system is the is only unit base system available in version 4.0.
Models from 3.5a that use base unit systems other than the SI system and include inputs that do not explicitly specify the units using the unit syntax will yield incorrect results, since those inputs will be incorrectly interpreted as SI units.
To correctly evaluate 3.5a models created with other base unit systems than the SI unit system, specify the unit using the unit syntax in all inputs in version 4.0.
Weak Constraints
Weak constraints are generally available in version 3.5a. In version 4.0, these constraints are defined in the physics interfaces.
There are some physics interfaces that are not able to define constraints as weak constraints; see the Backwards Compatibility sections for the modules below.
Models using weak constraints in version 3.5a, where the corresponding physics interface in 4.0 lacks these constraints, have to be manually changed to strong constraints. You can also rewrite such constraints using weak equations.
Axisymmetric Models
In version 3.5a equations in axisymmetric application modes use the independent variable for the radius, r, to account for axisymmetry. In version 4.0, the equations are compensated by using the factor 2πr.
If you have manually multiplied expressions by 2π for a version 3.5a model, please note that these may be incorrect when the model is opened in version 4.0.
Display of Equations
The equations for the physics interfaces are not displayed graphically in version 4.0. However, using dynamic help, you can get an overview of the equations formulated by a physics interface by just one click. Full support for display of equations is planned for version 4.1.
Report Generator
The report generator is not yet implemented in version 4.0. A report generator is planned for 4.1.