Equations
Equation entities contain mathematical equations that define more complex loads. They are used to define linear constraints in local and global coordinate systems.
Every equation must be organized into one load collector, and therefore are mutually exclusive to a load collector.
Equations are displayed as lines between the dependent node and the independent node(s) with EQ displayed at the dependent node of the equation in the modeling window.
Equations are used in Nastran as MPC (Multipoint Constraint Equation) or in Abaqus as *equation.
Equations are organized into load collectors.
Abaqus Cards
Card  Description 

*EQUATION  Define linear multipoint constraints. Note: Explicit node IDs are supported.
Node sets are not supported.
Equations are considered as loads and therefore, they are collected in load collectors. Upon export, they write to the bulk data portion of the Abaqus deck. 
ANSYS Cards
Card  Description 

CE  Defines a constraint equation relating to degrees of freedom. 
LSDYNA Cards
Several load types cause three cards to be output for x, y, and z components. During input, these are grouped into one load. Loads cannot be applied to sets, components, or boxes. Load curves are input and output. Use the Card Editor to select load curves. Unless mentioned in the Notes column, load cards cannot be edited.
Card  Description 

*CONSTRAINED_LINEAR  Define linear constraint equations between displacements and rotations, which can be defined in a local coordinate system. 
*CONSTRAINED_LINEAR_GLOBAL  Define linear constraint equations between displacements and rotations, which can be defined in global coordinate systems. 
Nastran Cards
Card  Description 

MPC  Defines a multipoint constraint equation of the form. Note: Individual weight
factors can be created on the nodes of an MPC equation using the update
functionality in the Equations panel.

OptiStruct Cards
Card  Description 

MPC  Defines a multipoint constraint equation of the
form. Note: Bulk Data
Entry

Permas Cards
Card  Description 

$MPC GENERAL  General linear constraint equation. 