% @(#)computdima.hlq	17.1.1.1 (ESO-IPG) 01/25/02 17:43:20 
%++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
%.COPYRIGHT  (c)  1990 European Southern Observatory
%.IDENT      computdima.hlq
%.AUTHOR     KB, IPG/ESO
%.KEYWORDS   MIDAS, help files, COMPUTE/DIMAGE
%.PURPOSE    On-line help file for the command: COMPUTE/DIMAGE
%.VERSION    1.0  19-MAR-1998 : Creation, KB
%----------------------------------------------------------------
\se
SECTION./DIMA
\es\co
COMPUTE/DIMAGE					19-MAR-1998  KB
\oc\su
COMPUTE/DIMAGE [outspec =] expression
	compute arithmetic expression
\us\pu
Purpose:  
           Perform arithmetic operations in double precision on constants 
           and images, using world coordinates.
\up\sub
Subject: 
           Double precision arithmetic
\bus\sy
Syntax: 
           COMPUTE/DIMAGE [outspec =] expression
\ys\pa
           outspec = frame to get result of expression. It will be created with
               the size of the common area of all images involved in the
               expression. The result frame will be created using double
               precision data format, no matter what data format the individual
               input frames have.
\\
               If "outspec =" is omitted, the expression should contain only
               numerical constants, the result of the computation is shown on
               the terminal and stored in double precision keyword OUTPUTD(1).
\\
               If descriptor copying is enabled (which is the default,
\\
               see also the command SET/MIDAS_SYSTEM DSCCOPY=..),
\\
               all non-standard descriptors of the 1. input frame in the
               expression are copied to the result frame unless you enter
               `frame,dscname' as outspec with dscname the name of a frame
               in the expression;
\\
               then, the non-standard descriptors of that frame are copied
               instead of the ones of the 1. frame in the expression
\ap\pa
           expression = arithmetic expression with up to 21 operands, which may
               be functions and frames or/and constants in the usual algebraic
               notation. Images must have same stepsize within 0.0001 of a step 
               and same origins within 0.05 of a step. Computations are done on
               the common area of all images only!
\ap\no
Note:      
           Spaces before and after the "=" sign are required. If the name of
           frame begins with a digit or contains a special char. like, e.g.
           `+',`-',... the name (with filetype!) has to be enclosed in double
           quotes.
\\
           Inside the expression may be spaces or not. However, if your
           expression is longer than 100 chars. (the current max. token length) 
           without spaces, you should include spaces between some operands,
           then the limit is 256 chars. for the complete command line.
\\
           If the result frame has the same name as a frame appearing in the
           expression, no new frame is created, but the result
           frame overwritten (also in VMS!). This option should be used with
           care, since computations are only done on the overlapping area of
           all frames in the expression!
\\
           Furthermore, since no new result frame is created, the final data is
           reconverted to the original data format when closing the result
           frame and you could get truncation errors!
\\
           The operations +, -, *, / and ** are supported with the same
           precedence as in FORTRAN. Parentheses may be used to change that
           order as well as to nest operations.
\\
           The functions
\\
           SQRT(a), EXP(a), EXP10(a), LN(a), LOG10(a), SIN(a) ASIN(a), COS(a),
           ACOS(a), TAN(a), ATAN(a), INT(a), ABS(a), ATAN2(a1,a2), MAX(a1,a2),
           MIN(a1,a2) and MOD(a1,a2)
\\
           are implemented as in FORTRAN. Except, that INT(a) will return the
           nearest integer of "a" converted to double. The trigonometric
           functions expect arguments in degrees!
\\
           Results of illegal operations (e.g. division by zero) are set to
           the "null value" stored in the real keyword NULL.
\on\sa
See also:
           COMPUTE/DPIXEL, COMPUTE/DPLANE, COMPUTE/IMAGE
\as\exs
Examples:
\ex
           COMPUTE/DIMA r = sqrt(c+5.-log10(b))+abs(aa)
             Compute resulting image `r.bdf' from the expression involving the
             frames `c.bdf', `b.bdf' and `aa.bdf'.
\\
             If descriptor copying is enabled, all non-standard descriptors of 
             `c.bdf' (the 1. frame in the expression) are copied to `r.bdf'.
\xe\ex
           COMPUTE/DIMA r,aa = sqrt(c + 5. - log10(b)) + abs(aa)
             As above, but if descriptor copying is enabled, all non-standard
             descriptors of `aa.bdf' are copied to `r.bdf'.
\xe\ex
           COMPUTE/DIMA EXP(25003.01/30001234.45678)+SIN(1.1)
             Compute the expression and store result in keyword OUTPUTD(1).
\xe\ex
           COMPUTE/DIMA 100011.13*{OUTPUTD(1)} + 4.001002005
             Use result from computation above.
\xe\ex
           COMPUTE/DIMA r = sqrt(c))+"qso+22.bdf"
             Compute resulting image `r.bdf' from the expression involving the
             frames `c.bdf' and `qso+22.bdf'. 
\xe\ex
           COMPUTE/DIMA a = a+LOG10(a)
             Also in VMS just modify frame `a.bdf', do not create a new file.
\xe \sxe