Lattice Expressions (expr)

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6.1.3 Lattice Expressions (expr)

Lattice expressions are strings that describe operations on a set of input images to form an output image. These strings use the Lattice Expression Language (LEL). LEL syntax is described in detail in AIPS++ Note 223

http://aips2.nrao.edu/docs/notes/223/223.html

ALERT: This document was written in the context of glish-based AIPS++ and is not yet updated to CASA syntax (see below).

The expr string contains the LEL expression:

expr       =      ’’   #  Mathematical expression using images

#          string containing LEL expression

#          A mathematical expression, with image file names.
#          image file names must be enclosed in double quotes (")
#          Default: none
#          Example: expr=’min("image2.im")+(2*max("image1.im"))’
#
#    Available functions in the expr and mask paramters:
#    pi(), e(), sin(), sinh(), asinh(), cos(), cosh(), tan(), tanh(),
#    atan(), exp(), log(), log10(), pow(), sqrt(), complex(), conj()
#    real(), imag(), abs(), arg(), phase(), aplitude(), min(), max()
#    round(), isgn(), floor(), ceil(), rebin(), spectralindex(), pa(),
#    iif(), indexin(), replace(), ...

For examples using LEL expr, see § 6.5.1 below. Note that in immath, shortcut names have been given to the images provided by the user in imagename that can be used in the LEL expression, for the above example:

imagename=[’image2.im’,’image1.im’]
expr=’min(IM0)+(2*max(IM1))’

ALERT: LEL expressions use 0-based indices. Also, the functions must be lowercase (in almost all cases we know about).

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