COMBINE
 This is part of the function module

Calculate a polynomial combination of a set of other variables.

The functional form of this function is

$C=\sum_{i=1}^{N_{arg}} c_i (x_i-a_i)^{p_i}$

The coefficients c, the parameters a and the powers p are provided as vectors.

Notice that COMBINE is not able to predict which will be periodic domain of the computed value automatically. The user is thus forced to specify it explicitly. Use PERIODIC=NO if the resulting variable is not periodic, and PERIODIC=A,B where A and B are the two boundaries if the resulting variable is periodic.

Examples

The following input tells plumed to print the distance between atoms 3 and 5 its square (as computed from the x,y,z components) and the distance again as computed from the square root of the square.

Click on the labels of the actions for more information on what each action computes
dist: DISTANCE =3,5
distance2: COMBINE =dist.x,dist.y,dist.z =2,2,2 =NO
distance: COMBINE =distance2 =0.5 =NO
PRINT =distance,distance2