Action: CONSTANT

Module	generic
Description	Usage
Create a constant value that can be passed to actions
output value	type
the constant value that was read from the plumed input	scalar/vector/matrix

Output components

This action can calculate the values in the following table when the associated keyword is included in the input for the action. These values can be referenced elsewhere in the input by using this Action's label followed by a dot and the name of the value required from the list below.

Further details and examples

Create a constant value that can be passed to actions

This action can be used to create constant scalars, vectors or matrices. These constants are assigned to a value, which can then be used later in the input. For example, the following input creates a value c and sets it equal to the constant value 4.5.

Click on the labels of the actions for more information on what each action computes

cThe CONSTANT action with label c calculates the following quantities:
 Quantity   
 Type   
 Description  
c
scalar
the constant value that was read from the plumed input: CONSTANTCreate a constant value that can be passed to actions This action has hidden defaults. More details VALUEthe single number that you would like to store=4.5
c: CONSTANTCreate a constant value that can be passed to actions This action uses the defaults shown here. More details VALUEthe single number that you would like to store=4.5  NROWS the number of rows in your input matrix=0 NCOLS the number of columns in your matrix=0
PRINTPrint quantities to a file. More details ARGthe labels of the values that you would like to print to the file=c STRIDE the frequency with which the quantities of interest should be output=1 FILEthe name of the file on which to output these quantities=constant_scalar

The output file printed by this input will contain a column in which every element is 4.5

By contrast, this input creates a five element vector called v with elements equal to 1, 2, 3, 4 and 5:

Click on the labels of the actions for more information on what each action computes

vThe CONSTANT action with label v calculates the following quantities:
 Quantity   
 Type   
 Description  
v
vector
the constant value that was read from the plumed input: CONSTANTCreate a constant value that can be passed to actions This action has hidden defaults. More details VALUESthe numbers that are in your constant value=1,2,3,4,5
v: CONSTANTCreate a constant value that can be passed to actions This action uses the defaults shown here. More details VALUESthe numbers that are in your constant value=1,2,3,4,5  NROWS the number of rows in your input matrix=0 NCOLS the number of columns in your matrix=0
PRINTPrint quantities to a file. More details ARGthe labels of the values that you would like to print to the file=v FILEthe name of the file on which to output these quantities=constant_vector

The PRINT action will now output a file with 6 columns. The first of these columns will be the time. Every element of the second column will be 1, every element of the second column will be 2 and so on.

Notice that can generate 5 scalar constant rather than a vector using an input like this:

Click on the labels of the actions for more information on what each action computes

cThe CONSTANT action with label c calculates the following quantities:
 Quantity   
 Type   
 Description  
c.v-0
scalar
the # value  This is the 0th of these quantities
c.v-1
scalar
the # value  This is the 1th of these quantities
c.v-2
scalar
the # value  This is the 2th of these quantities
c.v-3
scalar
the # value  This is the 3th of these quantities
c.v-4
scalar
the # value  This is the 4th of these quantities: CONSTANTCreate a constant value that can be passed to actions This action has hidden defaults. More details VALUESthe numbers that are in your constant value=1,2,3,4,5 SCALARS treat the input list of numbers as a set of scalars
c: CONSTANTCreate a constant value that can be passed to actions This action uses the defaults shown here. More details VALUESthe numbers that are in your constant value=1,2,3,4,5 SCALARS treat the input list of numbers as a set of scalars  NROWS the number of rows in your input matrix=0 NCOLS the number of columns in your matrix=0
PRINTPrint quantities to a file. More details ARGthe labels of the values that you would like to print to the file=c.v-0,c.v-1,c.v-2,c.v-3,c.v-4 FILEthe name of the file on which to output these quantities=five_scalars

or you can use five separate constant actions like this:

Click on the labels of the actions for more information on what each action computes

c1The CONSTANT action with label c1 calculates the following quantities:
 Quantity   
 Type   
 Description  
c1
scalar
the constant value that was read from the plumed input: CONSTANTCreate a constant value that can be passed to actions This action has hidden defaults. More details VALUEthe single number that you would like to store=1
c1: CONSTANTCreate a constant value that can be passed to actions This action uses the defaults shown here. More details VALUEthe single number that you would like to store=1  NROWS the number of rows in your input matrix=0 NCOLS the number of columns in your matrix=0
c2The CONSTANT action with label c2 calculates the following quantities:
 Quantity   
 Type   
 Description  
c2
scalar
the constant value that was read from the plumed input: CONSTANTCreate a constant value that can be passed to actions This action has hidden defaults. More details VALUEthe single number that you would like to store=2
c2: CONSTANTCreate a constant value that can be passed to actions This action uses the defaults shown here. More details VALUEthe single number that you would like to store=2  NROWS the number of rows in your input matrix=0 NCOLS the number of columns in your matrix=0
c3The CONSTANT action with label c3 calculates the following quantities:
 Quantity   
 Type   
 Description  
c3
scalar
the constant value that was read from the plumed input: CONSTANTCreate a constant value that can be passed to actions This action has hidden defaults. More details VALUEthe single number that you would like to store=3
c3: CONSTANTCreate a constant value that can be passed to actions This action uses the defaults shown here. More details VALUEthe single number that you would like to store=3  NROWS the number of rows in your input matrix=0 NCOLS the number of columns in your matrix=0
c4The CONSTANT action with label c4 calculates the following quantities:
 Quantity   
 Type   
 Description  
c4
scalar
the constant value that was read from the plumed input: CONSTANTCreate a constant value that can be passed to actions This action has hidden defaults. More details VALUEthe single number that you would like to store=4
c4: CONSTANTCreate a constant value that can be passed to actions This action uses the defaults shown here. More details VALUEthe single number that you would like to store=4  NROWS the number of rows in your input matrix=0 NCOLS the number of columns in your matrix=0
c5The CONSTANT action with label c5 calculates the following quantities:
 Quantity   
 Type   
 Description  
c5
scalar
the constant value that was read from the plumed input: CONSTANTCreate a constant value that can be passed to actions This action has hidden defaults. More details VALUEthe single number that you would like to store=5
c5: CONSTANTCreate a constant value that can be passed to actions This action uses the defaults shown here. More details VALUEthe single number that you would like to store=5  NROWS the number of rows in your input matrix=0 NCOLS the number of columns in your matrix=0
PRINTPrint quantities to a file. More details ARGthe labels of the values that you would like to print to the file=c1,c2,c3,c4,c5 FILEthe name of the file on which to output these quantities=five_scalars

Lastly, if you want to create a constant $2\times 3$ matrix you would use an input like the one below:

Click on the labels of the actions for more information on what each action computes

cThe CONSTANT action with label c calculates the following quantities:
 Quantity   
 Type   
 Description  
c
matrix
the constant value that was read from the plumed input: CONSTANTCreate a constant value that can be passed to actions More details VALUESthe numbers that are in your constant value=1,2,3,4,5,6 NROWS the number of rows in your input matrix=2 NCOLS the number of columns in your matrix=3
PRINTPrint quantities to a file. More details ARGthe labels of the values that you would like to print to the file=c FILEthe name of the file on which to output these quantities=constant_matrix

The constant matrix that this action generates is as follows:

$$M = \left( \begin{matrix} 1 & 2 & 3 \\ 4 & 5 & 6 \end{matrix} \right)$$

The print action ensures that the six elements of this constant matrix are output on every step.

The CONSTANT action is useful in combination with functions that take in input constants or parameters. For example, the following input instructs plumed to compute the distance between atoms 1 and 2. If this distance is between 1.0 and 2.0, it is printed. If it is lower than 1.0 (larger than 2.0), 1.0 (2.0) is printed

Click on the labels of the actions for more information on what each action computes

cnThe CONSTANT action with label cn calculates the following quantities:
 Quantity   
 Type   
 Description  
cn.v-0
scalar
the # value  This is the 0th of these quantities
cn.v-1
scalar
the # value  This is the 1th of these quantities: CONSTANTCreate a constant value that can be passed to actions This action has hidden defaults. More details VALUESthe numbers that are in your constant value=1.0,2.0 SCALARS treat the input list of numbers as a set of scalars
cn: CONSTANTCreate a constant value that can be passed to actions This action uses the defaults shown here. More details VALUESthe numbers that are in your constant value=1.0,2.0 SCALARS treat the input list of numbers as a set of scalars  NROWS the number of rows in your input matrix=0 NCOLS the number of columns in your matrix=0
disThe DISTANCE action with label dis calculates the following quantities:
 Quantity   
 Type   
 Description  
dis
scalar
the DISTANCE between this pair of atoms: DISTANCECalculate the distance/s between pairs of atoms. More details ATOMSthe pair of atom that we are calculating the distance between=1,2
sssThe SORT action with label sss calculates the following quantities:
 Quantity   
 Type   
 Description  
sss.1
scalar
the 1th largest of the input scalars
sss.2
scalar
the 2th largest of the input scalars
sss.3
scalar
the 3th largest of the input scalars: SORTThis function can be used to sort colvars according to their magnitudes. More details ARGthe values input to this function=cn.v-0,dis,cn.v-1
PRINTPrint quantities to a file. More details ARGthe labels of the values that you would like to print to the file=sss.2

By contrast this input only prints the distance between atom 1 and 2 if it is less than 1.

Click on the labels of the actions for more information on what each action computes

cnThe CONSTANT action with label cn calculates the following quantities:
 Quantity   
 Type   
 Description  
cn
scalar
the constant value that was read from the plumed input: CONSTANTCreate a constant value that can be passed to actions This action has hidden defaults. More details VALUEthe single number that you would like to store=1.0
cn: CONSTANTCreate a constant value that can be passed to actions This action uses the defaults shown here. More details VALUEthe single number that you would like to store=1.0  NROWS the number of rows in your input matrix=0 NCOLS the number of columns in your matrix=0
disThe DISTANCE action with label dis calculates the following quantities:
 Quantity   
 Type   
 Description  
dis
scalar
the DISTANCE between this pair of atoms: DISTANCECalculate the distance/s between pairs of atoms. More details ATOMSthe pair of atom that we are calculating the distance between=1,2
sssThe SORT action with label sss calculates the following quantities:
 Quantity   
 Type   
 Description  
sss.1
scalar
the 1th largest of the input scalars
sss.2
scalar
the 2th largest of the input scalars: SORTThis function can be used to sort colvars according to their magnitudes. More details ARGthe values input to this function=cn,dis
PRINTPrint quantities to a file. More details ARGthe labels of the values that you would like to print to the file=sss.1

Lastly, note that if you have an action that only takes constant values in input its output values will be treated as constants. For example, in the following input the values d and f are evaluated on every step. c, however, is only evaluated once during start up.

Click on the labels of the actions for more information on what each action computes

pThe CONSTANT action with label p calculates the following quantities:
 Quantity   
 Type   
 Description  
p
scalar
the constant value that was read from the plumed input: CONSTANTCreate a constant value that can be passed to actions This action has hidden defaults. More details VALUEthe single number that you would like to store=1.0
p: CONSTANTCreate a constant value that can be passed to actions This action uses the defaults shown here. More details VALUEthe single number that you would like to store=1.0  NROWS the number of rows in your input matrix=0 NCOLS the number of columns in your matrix=0
cThe CUSTOM action with label c calculates the following quantities:
 Quantity   
 Type   
 Description  
c
scalar
an arbitrary function: CUSTOMCalculate a combination of variables using a custom expression. More details ARGthe values input to this function=p FUNCthe function you wish to evaluate=2*x+1 PERIODICif the output of your function is periodic then you should specify the periodicity of the function=NO
dThe DISTANCE action with label d calculates the following quantities:
 Quantity   
 Type   
 Description  
d
scalar
the DISTANCE between this pair of atoms: DISTANCECalculate the distance/s between pairs of atoms. More details ATOMSthe pair of atom that we are calculating the distance between=1,2
fThe CUSTOM action with label f calculates the following quantities:
 Quantity   
 Type   
 Description  
f
scalar
an arbitrary function: CUSTOMCalculate a combination of variables using a custom expression. More details ARGthe values input to this function=p,d FUNCthe function you wish to evaluate=x*y PERIODICif the output of your function is periodic then you should specify the periodicity of the function=NO
PRINTPrint quantities to a file. More details ARGthe labels of the values that you would like to print to the file=f FILEthe name of the file on which to output these quantities=colvar STRIDE the frequency with which the quantities of interest should be output=1

Syntax

The following table describes the keywords and options that can be used with this action