The | Command

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Command Summary

Substitutes a value for a variable temporarily.

Command Syntax

expression

Menu Location

Press the

Calculator Compatibility

This command works on all calculators.

Token Size

1 byte

The | operator (which nobody seems to know how to pronounce, although TI suggests "with") temporarily sets a variable to some value, just for a single evaluation. For example:

:x^2+2x+1|x=5
           6

Using the | operator doesn't actually affect the value of the variable. However, it will work both if the variable is undefined, and if the variable already has a different value.

Only one | can occur in a single expression: if you have more, this will either cause an error or ignore all but the first substitution, depending on placement. However, one | is enough for any number of variables: just separate the values to use with and:

:x+y|x=2 and y=2
           4

Advanced Uses

The | operator has a more complicated use: rather than giving a specific value for a variable, you might give a condition (or several conditions) for its value, using the >, ≥, <, and ≤ operators. This condition will be used if it helps simplify the expression, especially with solve(). For instance:

:abs(x)|x<0
           -x

Weird things can happen if you do this to a variable whose value is already defined, however:

:5→x
           5
:abs(x)|x<0
           |undef|

Optimization

If a complicated expression has a repeating element, you may be able to make the calculation smaller and faster by replacing this repeating element with a variable, for which you substitute the correct value. For example (here the repeating element is √(1-x^2)):

:x√(1-x^2)+tanֿ¹(x/√(1-x^2))

can be

:x*a+tanֿ¹(x/a)|a=√(1-x^2)

A related trick is to make a substitution with a function, for an operation that has to be done several times in a single line. For example:

:a*(a-1)/2+b*(b-1)/2+c*(c-1)/2

can be

:f(a)+f(b)+f(c)|f(x)=x*(x-1)/2

Error Conditions

200 - Constraint expression invalid happens when the condition doesn't make sense to the calculator.

Related Commands

• →
• Local