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.help tcalc Jan92 ttools
.ih
NAME
tcalc -- Perform arithmetic operations on table columns.
.ih
USAGE
tcalc table outcol equals
.ih
DESCRIPTION
This task evaluates an arbitrary expression that includes column names,
constants, and operators, and creates a specified column in the
table---or overwrites an existing column if the specified name already exists.
Variables in the expression are column names in either case.
Columns
may be of any type except string. If the column name contains
non-alphanumeric characters, it should be preceded by a dollar sign
and followed by a blank. For example, the expression "date-obs+1."
contains the column "date-obs", but the task thinks that it contains
two column names, "date" and "obs". To ensure that the expression is
evaluated correctly, rewrite it as "$date-obs +1.". The variable
"rownum" may also be used in an expression if there is no column in
the table of the same name. Its value is the current row number. The
expression will be evaluated using the data types of the columns and
constants in the expression, with the usual rules of type promotion used in
Fortran. Please remember that integer division truncates.
The output value in any row will be set to INDEF if one or more column
values used in the calculation is equal to INDEF. The result will be
INDEF if either of the clauses in an if expression contains a row with
an INDEF value. If the result of an operation is undefined (such as
division by zero) the output column will also be set to INDEF.
The following Fortran-type arithmetic operators are supported. If the
second argument of the exponentiation is not an integer, the result
will be undefined if the first argument is not positive. Again,
remember that integer division truncates.
.nf
+ addition - subtraction
* multiplication / division
- negation ** exponentiation
.fi
The following logical operators are supported. Logical operators will
return a value of 1 if true or 0 if false. Logical operators are
supported in both their Fortran and SPP form.
.nf
.or. || logical or .and. && logical and
.eq. == equality .ne. != inequality
.lt. < less than .gt. > greater than
.le. <= less or equal .ge. >= greater or equal
.not. ! not
.fi
The following functions are supported. These functions all take a
single argument, which may be an expression. The argument or result of
trigonometric functions are in radians.
.nf
abs absolute value acos arc cosine
asin arc sine atan arc tangent
cos arc cosine cosh hyperbolic cosine
cube third power double convert to double
exp E raised to power int convert to integer
log natural logarithm log10 common logarithm
nint nearest integer real convert to real
sin sine sinh hyperbolic sine
sqr second power sqrt square root
tan tangent tanh hyperbolic tangent
.fi
The following functions take two arguments.
.nf
atan2 arc tangent dim positive difference
max maximum min minimum
mod modulus sign sign transfer
.fi
Conditional expressions of the form "if expr then expr else expr" are
supported. The expression after the else may be another conditional
expression. The words "if", "then", and "else" must be surrounded by
blanks.
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PARAMETERS
.ls table [file name template]
The input table, or tables; these files are modified in-place.
Results will be written to a new column in the table unless an
existing column name is specified, in which case the existing values
will be overwritten.
.le
.ls outcol [string]
Output column name. This is the column where results are written.
Caution: if this column already exists, then it will be overwritten
with the results of the calculation. Note that column names are not
case sensitive.
.le
.ls equals [string]
The arithmetic expression to evaluate. If the expression is too long
to pass as a parameter, place the expression in a file and set the
value of this parameter to the file name preceded by an "@", for
example, "@filename".
.le
.ls (datatype = real) [string, allowed values: real | double | int ]
Type of data stored in the output column, if it is a new column.
.le
.ls (colunits) [string]
Units for the output column, if it is a new column. This parameter
may be blank.
.le
.ls (colfmt) [string]
Print format for the output column, if it is a new column. If this
parameter is left blank then a default will be used. Type "help
ttools opt=sysdoc" for more information about print formats.
.le
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EXAMPLES
1. Create a column called 'FLUX', which will contain a value equal to
10.0**(-x/2.5) where x is the value in the column 'MAG'. The new
column will contain single precision data.
.nf
tt> tcalc "intab" "FLUX" "10.0**(-mag/2.5)"
.fi
2. Create a column called 'POLY', which will contain a value equal to
x+x**2 where x is the row number in the table.
.nf
tt> tcalc "test" "POLY" "rownum+sqr(rownum)"
.fi
3. Set quotient to zero where divison by zero would otherwise occur:
.nf
tt> tcalc "test" "QUOT" "if y != 0 then x / y else 0."
.fi
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BUGS
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REFERENCES
This task was written by Bernie Simon.
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SEE ALSO
imcalc
Type "help ttools opt=sys" for a higher-level description of the 'tables'
package.
.endhelp
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