NAME

tawk - extension to the awk programming language.

DESCRIPTION

tawk is an extended version of the awk programming langauge. It is based on the mawk implementation. The extensions are intended to make processing data files in astronomy easier.

EXTENSIONS

Sexagesimal Notation
In the text of a program or expression run by table, compute or calc (and others) a number may be represented in sexagesimal notation. In this context the number must form a single lexical token ie it cannot contain spaces. In a data table the degrees mininutes and seconds portions of the number may be separated by spaces.
```
                DDD:MM:SS.SSS
                 HH:MM:SS.SSS

                000d00m00.000
                 00h00m00.000

                    00:00.000
                    00m00.000
```
The sexagesimal number notation is supported in the printf function with a new format specifier "@".
```
        john@panic: @reckon 'printf("%2.2@\n", 21.5)'
        21:30:00
```
In addition to allowing sexagesimal notation the ASCII representation base of a number is tracked as an expression is evaluated. The output representation of an expression is that of the right most term in the expression. This feature is very handy in maintaining the representation of data files as they are operated on. It can also be used to convert data from one ASCII representation to another by adding 0 in a specific representation to the data to be converted.

Representation Zero

Decimal 0

Sexagesimal 0:00:00.00

Hexadecimal 0x0000

Octal 0o000

Binary 0b000

An example of converting an RA,Dec in decimal to an RA in sexagesimal representation.
```
   john@panic: @calc 12.5+0:00:00
   12:30:00.000
```

Representation	Zero
Decimal	0
Sexagesimal	0:00:00.00
Hexadecimal	0x0000
Octal	0o000
Binary	0b000

Additional functions

Units conversions

degrees = r2d(radians)
radians = d2r(degrees)
hours = r2h(radians)
radians = h2r(hours)
hours = d2h(degrees)
degrees = h2d(hours)

Astronomical Functions

Airmass
```
        mass = airmass(zd)
```
The airmass at a specific zenith distance is returned. Zenith distance is given in degrees. See slaAirmas.
Coordinate Precession
```
        [ra, dec] = precess(system, epoch0, epoch1, ra0, dec0)
```
The ra, dec of ra0, dec0 precessed from epoch0 to epoch1 is returned. The system may be one of "FK4" or "FK5". RA values are given and returned in hours. Dec values are given and returned in degrees. See slaPreces.
Standard Coordinate Systems Conversion
```
        
        [r2000, d2000] = fk45z(r1950, d1950, bepoch)
        [r2000, d2000, dr2000, dd2000, p2000, v2000] = fk425(r1950, d1950, dr1950, dd1950, p1950, v1950)

        [r1950, d1950, dr1950, dd1950] = fk54z(r2000, d2000, bepoch)
        [r1950, d1950, dr1950, dd1950, p1950, v1950] = fk524(r2000, d2000, dr2000, dd2000, p2000, v2000)
```
With fk425 and fk45z the Besellian r1950, d1950 coordinates in hours and degrees are converted to Julian r2000, d2000 coordiantes. Catalog data for proper motion, paralax and velocity may optionally be provided and will be returned. See slaFk425 and slaFk45z.
With fk524 and fk54z the Julian r2000, d2000 coordinates in hours and degrees are converted to Besellian r1950, d1950 coordiantes. Catalog data for proper motion, paralax and velocity may optionally be provided and will be returned. See slaFk524 and slaFk54z.
Tangent Plane Coordinates
```
        [r, d] = tp2s(x, y, rzero, dzero, scale, rot)
        [x, y] = s2tp(r, d, rzero, dzero, scale, rot)
```
Conversion bewteen spherical and tangent plane coordiantes. tp2s converts from tangent plane to sphreical coordinates with s2tp converting back. Each routine passes r and d as hours and degress. The additional parameters rzero, dzero, scale, rot define the zero point, scale and rotaiton of the tangent plane. rzero, dzero are given in hours and degrees. See slaDtp2s and slaDs2tp
Separation and Bearing Angles
```
        angle = sep(ra0, dec0, ra1, dec1)
        angle = bear(ra0, dec0, ra1, dec1)
```
Bear returns the bearing angle in degrees between to two ras and decs given in hours and degrees.
Sep returns the separation angle in degrees between to two ras and decs given in hours and degrees.
Modified Julain Date
```
        daynumber = mjd(datestring)
        daynumber = mjd(month, day, year)
        daynumber = mjd(month, day, year, hour, min, sec)
```
Convert from a calendar date to a modified julian day number with fractional time of day. All input dates are considered to be in GMT unless specifically overridden. This is only possible using a date string input. The syntax for converting the date string is explained here getdate .
UNIX Time
seconds = unx(datestring)
Convert from a calendar date to the number of seconds since the UNIX epoch (1970). All input dates are considered to be in GMT unless specifically overridden. This is only possible using a date string input. The syntax for converting the date string is explained here getdate .
Calendar date string creating
```
        datestring = cal(mjd)
        datestring = cal(mjd, format)
```
Convert from a modified julain date to a calendar date string. An optional format string may be provided. The format string is passed directly to the strftime function. Since strftime is a UNIX function it may not work for all formats before the UNIX epoch. Specifically it has been found that the day of the week is formatted as a "?" for these dates

Observing Station Parameters

        [name, westlong, lat, elevation] = obs(place)

Return earth position parameters of an observing station. See slaObs. Here is the current table of station data.

ID	Station	WestLong	Lat	Elevation
AAT	Anglo-Australian 3.9m Telescope	-2.602	-0.546	1164.000
LPO4.2	William Herschel 4.2m Telescope	0.312	0.502	2332.000
LPO2.5	Isaac Newton 2.5m Telescope	0.312	0.502	2336.000
LPO1	Jacobus Kapteyn 1m Telescope	0.312	0.502	2364.000
LICK120	Lick 120 inch	2.123	0.652	1290.000
MMT	MMT, Mt Hopkins	1.935	0.553	2608.000
VICBC	Victoria B.C. 1.85 metre	2.154	0.847	238.000
DUPONT	Du Pont 2.5m Telescope, Las Campanas	1.234	-0.506	2280.000
MTHOP1.5	Mt Hopkins 1.5 metre	1.935	0.553	2344.000
STROMLO74	Mount Stromlo 74 inch	-2.601	-0.616	767.000
ANU2.3	Siding Spring 2.3 metre	-2.602	-0.546	1149.000
GBVA140	Greenbank 140 foot	1.393	0.671	881.000
TOLOLO4M	Cerro Tololo 4 metre	1.236	-0.526	2235.000
TOLOLO1.5M	Cerro Tololo 1.5 metre	1.236	-0.526	2225.000
TIDBINBLA	Tidbinbilla 64 metre	-2.600	-0.618	670.000
BLOEMF	Bloemfontein 1.52 metre	-0.461	-0.507	1387.000
BOSQALEGRE	Bosque Alegre 1.54 metre	1.127	-0.551	1250.000
FLAGSTF61	USNO 61 inch astrograph, Flagstaff	1.950	0.614	2316.000
LOWELL72	Perkins 72 inch, Lowell	1.947	-0.613	2198.000
HARVARD	Harvard College Observatory 1.55m	1.249	0.742	185.000
OKAYAMA	Okayama 1.88 metre	-2.332	0.603	372.000
KPNO158	Kitt Peak 158 inch	1.948	0.558	2120.000
KPNO90	Kitt Peak 90 inch	1.948	0.558	2071.000
KPNO84	Kitt Peak 84 inch	1.948	0.558	2096.000
KPNO36FT	Kitt Peak 36 foot	1.948	0.558	1939.000
KOTTAMIA	Kottamia 74 inch	-0.555	0.522	476.000
ESO3.6	ESO 3.6 metre	1.234	-0.511	2428.000
MAUNAK88	Mauna Kea 88 inch	2.714	0.346	4215.000
UKIRT	UK Infra Red Telescope	2.713	0.346	4200.000
QUEBEC1.6	Quebec 1.6 metre	1.242	0.793	1114.000
MTEKAR	Mt Ekar 1.82 metre	-0.202	0.800	1365.000
MTLEMMON60	Mt Lemmon 60 inch	1.932	0.566	2790.000
MCDONLD2.7	McDonald 2.7 metre	1.816	0.535	2075.000
MCDONLD2.1	McDonald 2.1 metre	1.816	0.535	2075.000
PALOMAR200	Palomar 200 inch	2.040	0.582	1706.000
PALOMAR60	Palomar 60 inch	2.040	0.582	1706.000
DUNLAP74	David Dunlap 74 inch	1.386	0.766	244.000
HPROV1.93	Haute Provence 1.93 metre	-0.100	0.767	665.000
HPROV1.52	Haute Provence 1.52 metre	-0.100	0.767	667.000
SANPM83	San Pedro Martir 83 inch	2.015	0.542	2830.000
SAAO74	Sutherland 74 inch	-0.363	-0.565	1771.000
TAUTNBG	Tautenburg 2 metre	-0.204	0.890	331.000
CATALINA61	Catalina 61 inch	1.933	0.566	2510.000
STEWARD90	Steward 90 inch	1.948	0.558	2071.000
USSR6	USSR 6 metre	-0.723	0.762	2100.000
ARECIBO	Arecibo 1000 foot	1.165	0.320	496.000
CAMB5KM	Cambridge 5km	-0.001	0.911	17.000
CAMB1MILE	Cambridge 1 mile	-0.001	0.910	17.000
EFFELSBERG	Effelsberg 100 metre	-0.120	0.882	366.000
GBVA300	Greenbank 300 foot	1.394	0.671	894.000
JODRELL1	Jodrell Bank 250 foot	0.040	0.929	78.000
PARKES	Parkes 64 metre	-2.588	-0.576	392.000
VLA	Very Large Array	1.878	0.595	2124.000
SUGARGROVE	Sugar Grove 150 foot	1.384	0.672	705.000
USSR600	USSR 600 foot	-0.726	0.765	973.000
NOBEYAMA	Nobeyama 45 metre	-2.417	0.627	1350.000
JCMT	JCMT 15 metre	2.714	0.346	4111.000
ESONTT	ESO 3.5 metre NTT	1.234	-0.511	2377.000
ST.ANDREWS	St Andrews	0.049	0.983	30.000
APO3.5	Apache Point 3.5m	1.847	0.572	2809.000
KECK1	Keck 10m Telescope 1	2.714	0.346	4160.000
KECK1	?	2.714	0.346	4160.000

Siderial Time
```
        stime = st(place, date)
```
Return the siderial time at place for the given datestring. See slaGmst, slaEqeqx.
Alt Az pointing direction
```
        [alt, az] = altax(place, ra, dec, datestring)
        [alt, az] = altax(place, ra, dec, datestring, epoch)
```
Return the altitude and azimuth for pointing a telescope at the ra, dec, given in hours and degrees. The place is given as the ID of an observing station. See slaMappa, slaAoppa, slaMapqkz, slaAopqk.
Gausian Residual
```
        x = gresid(s)
```
The results of many calls to this routine will be normally distributed with mean zero and standard deviation s.
The Box-Muller algorithm is used. This is described in Numerical Recipes, Section 7.2. See slaGresid

Multiple function value return and assignment lists:
To support returning multiple values as is convient in the above functions, the awk syntax has been extended to allow returning a list of values.
```
        [ x, y, z ] = funct()
```
This works for user defined functions as well:
```
                function squares(x, y) {
                        return [ x * x, y * y ]
                }
```
The bracket notation in the return statement allows a list of expressions to be returned from the function. When the function is called it should be called from an assignment list statment.
```
                [ xsq, ysq ] = squares(x, y)
```
Here the bracket notation to the left of an assignment allows the multiple values returning from the function to be assigned to variables.
Multiple assignment is also supported.
```
        [ x, y, z ] = [ z, y, x ]
```

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