MOLPRO

8 VARIABLES 51
The current length of an array can be accessed by preceding # to the variable name. For instance,
in the above examples #R and #METHOD have the values 5 and 4, respectively. If a variable is
not defined, zero is returned but no error occurs. This can be used to test for the existence of a
variable, for example:
IF(#SPIN.EQ.0.AND.#NELEC.EQ.1) SET,SPIN=MOD(NELEC,2)
This defines variable SPIN if it is unknown and if NELEC is a scalar (one dimensional) variable.
8.7 Vector operations
The following simple vector operations are possible:
• Copying or appending a vector to another vector. For instance S=R copies a vector R
to a vector S. S(3)=R copies R to S(3), S(4), .... S(#S+1)=R appends vector
R to vector S. It is also possible to access a range of subsequent elements in a vector:
S=R(2:4) copies elements 2 to 4 of R to S(1), S(2), S(3). Note that R(2:)
denotes elements R(2) to R(#R), but R(2) denotes a single element of R.
• Vector-scalar operations: R=R*2 multiplies each element of R by 2. Instead of the number
2, also scalar (one dimensional) variables or expressions can be used, e.g., R=R*ANG
converts all elements of R from Ångstrøm to bohr, or Z=R*COS(THETA) creates a vector
Z with elements Z(i) = R(i)*COS(THETA). All other algebraic operators can be
used instead of “*”.
• Vector-vector operations: If A and B are vectors of the same length, then A × B is also a
vector of this length. Here × stands for any algebraic operator, and the operation is done
for each pair of corresponding elements. For instance, A + B adds the vectors A and B,
and A * B multiplies their elements. Note that the latter case is not a scalar product. If
an attempt is made to connect two vectors of different lengths by an algebraic operator,
an error occurs.
• Intrinsic functions: Assume THETA=[100,110,120,-130] to be a vector of angles
(in degrees). In this case X=2*COS(THETA) is also a vector containing the cosines of
each element of THETA multiplied by two, i.e., X(i) = 2*COS(THETA(i)). MAX(THETA)
or MIN(THETA) return the maximum and minimum values, respectively, in array THETA.
Vector operations can also be nested, e.g., MAX(ABS(THETA)) returns the maximum
value in array ABS(THETA).
At present, vector operations are not supported with string variables.
8.8 Special variables
8.8.1 Variables set by the program
A number of variables are predefined by the program. The following variables can be used to
convert between atomic units and other units:
EV=1.d0/27.2113961d0 HARTREE
KELVIN=1.d0/3.157733d5 HARTREE
KJOULE=1.d0/2625.500d0 HARTREE
KCAL=1.d0/627.5096d0 HARTREE