<I>equal</I> or <I>atom</I> args = one formula containing numbers, thermo keywords, math operations, group functions, atom values and vectors, compute/fix/variable references

    numbers = 0.0, 100, -5.4, 2.8e-4, etc

    thermo keywords = vol, ke, press, etc from <A HREF = "thermo_style.html">thermo_style</A>

    math operations = (), -x, x+y, x-y, x*y, x/y, x^y, sqrt(x), exp(x), ln(x), ceil(x), floor(x), round(x)

    math operations = (), -x, x+y, x-y, x*y, x/y, x^y, 

                      sqrt(x), exp(x), ln(x), log(x),

                      sin(x), cos(x), tan(x), asin(x), acos(x), atan(x),

                      ceil(x), floor(x), round(x)

    group functions = count(group), mass(group), charge(group),

		      xcm(group,dim), vcm(group,dim), fcm(group,dim),

		      bound(group,xmin), gyration(group)

<DIV ALIGN=center><TABLE  BORDER=1 >

<TR><TD >Number</TD><TD > 0.2, 100, 1.0e20, -15.4, etc</TD></TR>

<TR><TD >Thermo keywords</TD><TD > vol, pe, ebond, etc</TD></TR>

<TR><TD >Math operations</TD><TD > (), -x, x+y, x-y, x*y, x/y, x^y, sqrt(x), exp(x), ln(x), ceil(x), floor(x), round(x)</TD></TR>

<TR><TD >Math operations</TD><TD > (), -x, x+y, x-y, x*y, x/y, x^y, sqrt(x), exp(x), ln(x), log(x), sin(x), cos(x), tan(x), asin(x), acos(x), atan(x), ceil(x), floor(x), round(x)</TD></TR>

<TR><TD >Group functions</TD><TD > count(ID), mass(ID), charge(ID), xcm(ID,dim),                  vcm(ID,dim), fcm(ID,dim), bound(ID,dir), gyration(ID)</TD></TR>

<TR><TD >Atom values</TD><TD > mass[N], x[N], y[N], z[N],              vx[N], vy[N], vz[N], fx[N], fy[N], fz[N]</TD></TR>

<TR><TD >Atom vectors</TD><TD > mass[], x[], y[], z[],               vx[], vy[], vz[], fx[], fy[], fz[]</TD></TR>

<P>Math operations are written in the usual way, where the "x" and "y" in

the examples above can be another section of the formula.  Operators

are evaluated left to right and have the usual precedence: unary minus

before exponentiation, exponentiation before multiplication and

before exponentiation ("^"), exponentiation before multiplication and

division, and multiplication and division before addition and

subtraction.  Parenthesis can be used to group one or more portions of

a formula and enforce a desired order of operations.  Additional math

operations can be specified as keywords followed by a parenthesized

argument, e.g. sqrt(v_ke).  The ceil(), floor(), and round()

operations are those in the C math library.  Ceil() is the smallest

integer not less than its argument.  Floor() if the largest integer

not greater than its argument.  Round() is the nearest integer to its

argument.

argument, e.g. sqrt(v_ke).  Note that ln() is the natural log; log()

is the base 10 log.  The ceil(), floor(), and round() operations are

those in the C math library.  Ceil() is the smallest integer not less

than its argument.  Floor() if the largest integer not greater than

its argument.  Round() is the nearest integer to its argument.

</P>

<P>Group functions take one or two arguments in a specific format.  The

first argument is the group-ID.  The <I>dim</I> argument, if it exists, is

  {equal} or {atom} args = one formula containing numbers, thermo keywords, math operations, group functions, atom values and vectors, compute/fix/variable references

    numbers = 0.0, 100, -5.4, 2.8e-4, etc

    thermo keywords = vol, ke, press, etc from "thermo_style"_thermo_style.html

    math operations = (), -x, x+y, x-y, x*y, x/y, x^y, sqrt(x), exp(x), ln(x), ceil(x), floor(x), round(x)

    math operations = (), -x, x+y, x-y, x*y, x/y, x^y, 

                      sqrt(x), exp(x), ln(x), log(x),

                      sin(x), cos(x), tan(x), asin(x), acos(x), atan(x),

                      ceil(x), floor(x), round(x)

    group functions = count(group), mass(group), charge(group),

		      xcm(group,dim), vcm(group,dim), fcm(group,dim),

		      bound(group,xmin), gyration(group)

Number: 0.2, 100, 1.0e20, -15.4, etc

Thermo keywords: vol, pe, ebond, etc

Math operations: (), -x, x+y, x-y, x*y, x/y, x^y, sqrt(x), exp(x), ln(x), ceil(x), floor(x), round(x)

Math operations: (), -x, x+y, x-y, x*y, x/y, x^y, sqrt(x), exp(x), ln(x), log(x), sin(x), cos(x), tan(x), asin(x), acos(x), atan(x), ceil(x), floor(x), round(x)

Group functions: count(ID), mass(ID), charge(ID), xcm(ID,dim), \

                 vcm(ID,dim), fcm(ID,dim), bound(ID,dir), gyration(ID)

Atom values: mass\[N\], x\[N\], y\[N\], z\[N\], \

Math operations are written in the usual way, where the "x" and "y" in

the examples above can be another section of the formula.  Operators

are evaluated left to right and have the usual precedence: unary minus

before exponentiation, exponentiation before multiplication and

before exponentiation ("^"), exponentiation before multiplication and

division, and multiplication and division before addition and

subtraction.  Parenthesis can be used to group one or more portions of

a formula and enforce a desired order of operations.  Additional math

operations can be specified as keywords followed by a parenthesized

argument, e.g. sqrt(v_ke).  The ceil(), floor(), and round()

operations are those in the C math library.  Ceil() is the smallest

integer not less than its argument.  Floor() if the largest integer

not greater than its argument.  Round() is the nearest integer to its

argument.

argument, e.g. sqrt(v_ke).  Note that ln() is the natural log; log()

is the base 10 log.  The ceil(), floor(), and round() operations are

those in the C math library.  Ceil() is the smallest integer not less

than its argument.  Floor() if the largest integer not greater than

its argument.  Round() is the nearest integer to its argument.

Group functions take one or two arguments in a specific format.  The

first argument is the group-ID.  The {dim} argument, if it exists, is