Symbolics > Working with Symbolics > Working with Variables > Making Assumptions about Variables
  
Making Assumptions about Variables
Use the keyword assume and one or more modifying expressions to make assumptions about the domain of a variable in a symbolic expression, such as restricting it to be a real number. The types of modifying expressions you can insert after assume follow:
Modifying Expression
Assumption
x = real
x is a real number.
x = integer
x is an integer.
x > a
x is a real number greater than a.
x ≥ a
x is a real number greater than or equal to a.
x < b
x is a real number less than b.
x ≤ b
x is a real number less than or equal to b.
x = RealRange(a, b)
x is a real number in the range a < x < b, where a < b.
n = even
n is an even integer.
n = odd
n is an odd integer.
Use the Boolean equal operator to specify the equalities in the preceding list.
The following rules apply for variables:
• If you insert assume after another keyword, the assumption on the variables applies to the operation performed by the first keyword.
• The keyword assume does not make an assignment or substitution. Use a variable definition or the keyword substitute for this purpose.
• To exclude or substitute numerically defined variables, use the keyword explicit. The keyword assume merely constrains the region over which PTC Mathcad finds a result, and is primarily useful for simplification and symbolic integration.
Examples
• To restrict the domain of x to real numbers use this expression:
• To restrict the domain of more than one variable in the expression, insert a comma-separated list of modifying expressions after the assume keyword:
• To restrict the domain of all variables in the expression, insert the modifier ALL in the modifying expression: