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Environment Variables

Description

• 

Environment variables can be used in a simple assignment.  In a procedure body, the assignment is automatically undone on exit from the procedure.  The value of the environment variable is available to all subprocedures called from that procedure, unless locally superseded.

• 

The following is a list of predefined environment variables:

%

%%

%%%

_ans

Digits

UseHardwareFloats

index/newtable

mod

Normalizer

NumericEventHandlers

Order

printlevel

Rounding

Testzero

 

 

 

 

 

 

• 

A variable with name beginning with "_Env" is considered an environment variable.

• 

 %, %%, and %%% are the results of the last, second last, and third last computation in the current environment.

• 

Digits is the number of significant digits used for floating-point operations, and is set to 10 initially.

• 

mod is set to `modp` initially.

• 

Normalizer is set to `normal` initially, and is used by the kernel in series to normalize leading terms of divisors.

• 

Order represents the order of series calculations performed by Maple. It does not represent the order of the series output. Order is set to 6 initially.

• 

The setting of printlevel causes the display of the results of all statements executed up to the level indicated by printlevel. Initially, printlevel is set to 1.

• 

Testzero is initialized with proc() evalb(Normalizer(args[1]) = 0) end proc, which is a relatively trivial test for zero.  Testzero is used in the kernel by series, when it needs to determine whether a leading coefficient is zero for division. In principle, every test for zero and every call to normal should be done using these functions.

• 

The call anames('environment') returns a sequence of all the currently active environment variables. Note that an _Env variable is not considered to be an environment variable at the top level; only once execution is inside a procedure is an environment set up to protect the top-level value of the variable. So, _Env variables only show up if these variables are modified within a procedure, and anames('environment') is called from within the procedure or at a deeper level of execution.

Examples

t := proc() Digits := Digits + 4;  end proc:

printDigits

10

(1)

During the execution of "t", Digits is increased by 4, and automatically reset on exit from "t".

t

14

(2)

printDigits

10

(3)

The following is an example of a user-defined environment variable.

_Envy:=foo

_Envy:=foo

(4)

p := proc() _Envy := bar end proc:

p

bar

(5)

_Envy

foo

(6)

anamesenvironment

Testzero,UseHardwareFloats,Rounding,%,_ans,%%%,Digits,index/newtable,mod,%%,Order,printlevel,Normalizer,NumericEventHandlers,_Envy

(7)

p := proc() _Envy := bar; anames(environment) end proc:

p

Testzero,UseHardwareFloats,Rounding,%,_ans,%%%,Digits,index/newtable,mod,%%,Order,printlevel,Normalizer,NumericEventHandlers,_Envy,_Envy

(8)

See Also

Digits, ditto, mod, normal, NumericEventHandler, Order, printlevel, Rounding, series, UseHardwareFloats


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