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=complex
|
x is a complex 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.
• By default, all variables in Mathcad are real. Use the complex modifier to indicate that a variable is complex:
• Mathcad assumes that only the variable t outside the function is complex.
• Use the All modifier to indicate that all t variables, including the one inside the function, are complex:
Examples
• To restrict the domain of x to real numbers use this expression:
• To restrict the domain of x to complex 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:
