free grads

()ave

ave(expr, dim1, dim2 <,tinc> <,-b>)

Averages the result of expr over the specified dimension range. If the averaging dimension is time, an optional time increment tincr may be specified.  

q attr

q attr <fnum>

This command returns all the attribute metadata associated with file number fnum in a formatted manner. If no value for fnum is given, then the attributes for the default file are returned. The output of 'q attr' may be read by the user in the command window, or parsed by a script for the purpose of capturing the metadata and including it in the analysis or display. There are three categories of attributes: (1) global, which means the attribute is relevant for all the data in the file, (2) coordinate, which means the attribute describes one of the four dimensions (lon, lat, lev, or time), or (3) variable, which means the attribute is assoicated with a particular variable in the file. The formatting of the attribute listing is as follows:  

()atot

Thie atot function (in grads version 2.0.2+) duplicates the summing capability of asum but adds the latitude-weighting feature of aave. The syntax is:

atot(expr, xdim1, xdim2, ydim1, ydim2)

()atan2

atan2 (expr1, expr2)

Applies the tan^-1 function to the result of (expr1/expr2).

If expr1 and expr2 are both zero, the result is arbitrarily set to zero. The result of the atan2 function is in radians.   

()asumg

asumg(expr, xdim1, xdim2, ydim1, ydim2)

This function is the same as asum in all respects except one: the sums are calculated without any weighting at all.  

()asum

This function takes a sum over an X-Y region. The syntax is:

asum(expr, xdim1, xdim2, ydim1, ydim2)

asin

asin(expr)

Applies the sin^-1 function to the result of expr. Values of expr that exceed 1 or are less than -1 are set to missing in the final result. The result of the asin function is in radians. 

ASCII or Text Data and grads

Input ASCII data

grads does not directly handle data in ASCII format -- there is no such thing as 'dtype ascii'. ASCII data must be converted to into one of the binary data formats that are handled by grads. There are many ways to do this with a variety of programming/scripting languages and tools. Below is a very simple example of how you could do it using a grads script.

Suppose you have an ascii file that contains a column of 100 numbers:  

set arrscl

set arrscl size <magnitude>

Specifies arrow length scaling. 

set arrowhead

set arrowhead size

where size is the size of the arrowhead. The default is 0.05. If set to 0, no arrowhead is plotted. If set to a negative value, the size of the arrowhead will be scaled to the size of the arrow. The value specified will be the size when the arrow is one inch in length. 

set arrlab

set arrlab on|off

Toggles drawing the vector arrow label for plots drawn with set gxout vector. The default is on and "sticks" until reset by another set arrlab command.   

set antialias

set antialias on | off

set annot

This command controls the look of plot annotations: the frame around the plot, any additional axes that are drawn alongside the frame, the axis labels and tick marks, and the grads logo and date stamp at the bottom of the page. 

Animation

()aminlocy

This function returns the Y location of minimum grid value over a spatial domain. The syntax is:

aminlocy(expr, xdim1, xdim2, ydim1, ydim2)

()aminlocx

This function returns the X location of minimum grid value over a spatial domain. The syntax is:

aminlocx(expr, xdim1, xdim2, ydim1, ydim2)

()amin

This function returns an area minimum -- the minimum value in a grid spanning an X-Y region. The syntax is:

amin(expr, xdim1, xdim2, ydim1, ydim2)

()amean

amean (expr, xdim1, xdim2, ydim1, ydim2)

()amaxlocy

This function returns the Y location of maximum grid value over a spatial domain. The syntax is:

amaxlocy(expr, xdim1, xdim2, ydim1, ydim2)

amaxlocx()

This function returns the X location of maximum grid value over a spatial domain. The syntax is:

amaxlocx(expr, xdim1, xdim2, ydim1, ydim2)

amax()

This function returns an area maximum -- the maximum value in a grid spanning an X-Y region. The syntax is:

amax(expr, xdim1, xdim2, ydim1, ydim2)

Using Templates

grads allows you use a single data descriptor file to aggregate multiple data files and handle them as if they were one individual file. The individual data files must be identical in the X, Y, and Z dimensions and have the same list of variables. The time range of each individual file must be indicated it its filename. Beginning with version 2.0, data files may also be aggregated in the ensemble dimension.  

acos(expr)

abs

abs(expr)

Takes the absolute value of the result of expr. Operates on both gridded and station data. Missing data values do not participate.  

This function takes an areal average over an X-Y region. The syntax is:

aave(expr, xdim1, xdim2, ydim1, ydim2)

where:

expr    - any valid grads expression 
xdim1   - starting X dimension expression 
xdim2   - ending X dimension expression 
ydim1   - starting Y dimension expression 
ydim2   - ending Y dimension expression