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Trace
Trace[
expr
] generates a list of all expressions used in the evaluation of expr.
Trace[
expr
,
form
] includes only those expressions which match form.
Trace[
expr
,
s
] includes all evaluations which use transformation rules associated with the symbol s.
In general, form in Trace[
expr
,
form
] is compared both with each complete expression that is evaluated, and with the tag associated with any transformation rule used in the evaluation.
Trace[
expr
,
lhs
->
rhs
] picks out expressions which match lhs, then replaces them with rhs in the list returned.
All expressions in the list returned by Trace are wrapped in HoldForm.
Trace returns a set of nested lists. Each individual list corresponds to a single evaluation chain, which contains the sequence of forms found for a particular expression. The list has sublists which give the histories of subsidiary evaluations.
Example: Trace[2 3 + 4] .
The following options can be given:
During the execution of Trace, the settings for the form argument, and for the options TraceOn and TraceOff, can be modified by resetting the values of the global variables $TracePattern, $TraceOn and $TraceOff, respectively.
See the Mathematica book: Section 2.5.4, Section 2.5.10.
See also: TraceDialog, TracePrint, TraceScan.
Further Examples
This show the order of operations in a simple arithmetic expression.
In[1]:= 
Out[1]= 
Here is the recursive definition of the Fibonacci numbers.
In[2]:= 
Here are the end conditions for the recursion.
In[3]:= 
Out[3]= 
This tells Trace to return only the arguments of fib used in the evaluation of fib[5].
In[4]:= 
Out[4]= 
This shows all occurrences of fib in the evaluation of fib[3].
In[5]:= 
Out[5]= 
THIS IS DOCUMENTATION FOR AN OBSOLETE PRODUCT. SEE THE DOCUMENTATION CENTER FOR THE LATEST INFORMATION. | | | |
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