MFILTER_MORE

This is part of the multicolvar module |

This action can be used to filter the distribution of colvar values in a MultiColvar so that one can compute the mean and so on for only those multicolvars more than a tolerance.

This action can be used to create a dynamic group of atom based on the value of a multicolvar. In this action a multicolvar is within the dynamic group if its value is greater than a target. In actuality a weight, \(w_i\) is ascribed to each colvar, \(s_i\) calculated by a multicolvar and this weight measures the degree to which a colvar is a member of the group. This weight is calculated using a switchingfunction , \(\sigma\) so it is given by:

\[ w_i = 1 - \sigma(s_i) \]

If one calculates a function of the set of multicolvars these weights are included in the calculation. As such if one calculates the MEAN, \(\mu\) of a filtered multicolvar what is computed is the following:

\[ \mu = \frac{ \sum_i w_i s_i }{ \sum_i w_i} \]

One is thus calculating the mean for those colvars that are greater than the target.

- Examples

The example shown below calculates the mean for those distances that greater than 1.5 nm in length

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

d1:DISTANCESGROUPA=1Calculate the distances between all the atoms in GROUPA and all the atoms in GROUPB.GROUPB=2-50Calculate the distances between all the atoms in GROUPA and all the atoms in GROUPB.MEANtake the mean of these variables.d4:MFILTER_MOREDATA=compulsory keywordThe multicolvar that calculates the set of base quantities that we are interested ind1SWITCH={GAUSSIAN D_0=1.5 R_0=0.00001}This keyword is used if you want to employ an alternative to the continuous switching function defined above.MEANtake the mean of these variables.

More complicated things can be done by using the label of a filter as input to a new multicolvar as shown in the example below. Here the coordination numbers of all atoms are computed. The atoms with a coordination number greater than 2 are then identified using the filter. This reduced list of atoms is then used as input to a second coordination number calculation. This second coordination number thus measures the number of two-coordinated atoms that each of the two-coordinated atoms is bound to.

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

c1:COORDINATIONNUMBERSPECIES=1-150this keyword is used for colvars such as coordination number.SWITCH={EXP D_0=4.0 R_0=0.5 D_MAX=6.0}This keyword is used if you want to employ an alternative to the continuous switching function defined above.cf:MFILTER_MOREDATA=compulsory keywordThe multicolvar that calculates the set of base quantities that we are interested inc1SWITCH={RATIONAL D_0=2.0 R_0=0.1}This keyword is used if you want to employ an alternative to the continuous switching function defined above.LOWMEM( default=off ) lower the memory requirementsc2:COORDINATIONNUMBERSPECIES=this keyword is used for colvars such as coordination number.cfMORE_THAN={RATIONAL D_0=2.0 R_0=0.1}calculate the number of variables more than a certain target value.

- Glossary of keywords and components

- Description of components

When the label of this action is used as the input for a second you are not referring to a scalar quantity as you are in regular collective variables. The label is used to reference the full set of quantities calculated by the action. This is usual when using MultiColvar functions. Generally when doing this the previously calculated multicolvar will be referenced using the DATA keyword rather than ARG.

This Action can be used to calculate the following scalar quantities directly. These quantities are calculated by employing the keywords listed below. These quantities can then be referenced elsewhere in the input file by using this Action's label followed by a dot and the name of the quantity. Some of them can be calculated multiple times with different parameters. In this case the quantities calculated can be referenced elsewhere in the input by using the name of the quantity followed by a numerical identifier e.g. *label*.lessthan-1, *label*.lessthan-2 etc. When doing this and, for clarity we have made it so that the user can set a particular label for each of the components. As such by using the LABEL keyword in the description of the keyword input you can customize the component name

Quantity | Keyword | Description |

vmean | VMEAN | the norm of the mean vector. The output component can be referred to elsewhere in the input file by using the label.vmean |

altmin | ALT_MIN | the minimum value. This is calculated using the formula described in the description of the keyword so as to make it continuous. |

highest | HIGHEST | the highest of the quantities calculated by this action |

lowest | LOWEST | the lowest of the quantities calculated by this action |

max | MAX | the maximum value. This is calculated using the formula described in the description of the keyword so as to make it continuous. |

mean | MEAN | the mean value. The output component can be referred to elsewhere in the input file by using the label.mean |

min | MIN | the minimum value. This is calculated using the formula described in the description of the keyword so as to make it continuous. |

moment | MOMENTS | the central moments of the distribution of values. The second moment would be referenced elsewhere in the input file using label.moment-2, the third as label.moment-3, etc. |

- Compulsory keywords

DATA | The multicolvar that calculates the set of base quantities that we are interested in |

NN | ( default=6 ) The n parameter of the switching function |

MM | ( default=0 ) The m parameter of the switching function; 0 implies 2*NN |

D_0 | ( default=0.0 ) The d_0 parameter of the switching function |

R_0 | The r_0 parameter of the switching function |

- Options

NUMERICAL_DERIVATIVES | ( default=off ) calculate the derivatives for these quantities numerically |

NOPBC | ( default=off ) ignore the periodic boundary conditions when calculating distances |

SERIAL | ( default=off ) do the calculation in serial. Do not use MPI |

LOWMEM | ( default=off ) lower the memory requirements |

TIMINGS | ( default=off ) output information on the timings of the various parts of the calculation |

VMEAN | calculate the norm of the mean vector. The final value can be referenced using label.vmean. You can use multiple instances of this keyword i.e. VMEAN1, VMEAN2, VMEAN3... The corresponding values are then referenced using label.vmean-1, label.vmean-2, label.vmean-3... |

MEAN | take the mean of these variables. The final value can be referenced using label.mean. You can use multiple instances of this keyword i.e. MEAN1, MEAN2, MEAN3... The corresponding values are then referenced using label.mean-1, label.mean-2, label.mean-3... |

MOMENTS | calculate the moments of the distribution of collective variables. The mth moment of a distribution is calculated using \(\frac{1}{N} \sum_{i=1}^N ( s_i - \overline{s} )^m \), where \(\overline{s}\) is the average for the distribution. The moments keyword takes a lists of integers as input or a range. Each integer is a value of \(m\). The final calculated values can be referenced using moment- \(m\). You can use the COMPONENT keyword in this action but the syntax is slightly different. If you would like the second and third moments of the third component you would use MOMENTS={COMPONENT=3 MOMENTS=2-3}. The moments would then be referred to using the labels moment-3-2 and moment-3-3. This syntax is also required if you are using numbered MOMENT keywords i.e. MOMENTS1, MOMENTS2... |

MIN | calculate the minimum value. To make this quantity continuous the minimum is calculated using \( \textrm{min} = \frac{\beta}{ \log \sum_i \exp\left( \frac{\beta}{s_i} \right) } \) The value of \(\beta\) in this function is specified using (BETA= \(\beta\)) The final value can be referenced using label.min. You can use multiple instances of this keyword i.e. MIN1, MIN2, MIN3... The corresponding values are then referenced using label.min-1, label.min-2, label.min-3... |

MAX | calculate the maximum value. To make this quantity continuous the maximum is calculated using \( \textrm{max} = \beta \log \sum_i \exp\left( \frac{s_i}{\beta}\right) \) The value of \(\beta\) in this function is specified using (BETA= \(\beta\)) The final value can be referenced using label.max. You can use multiple instances of this keyword i.e. MAX1, MAX2, MAX3... The corresponding values are then referenced using label.max-1, label.max-2, label.max-3... |

ALT_MIN | calculate the minimum value. To make this quantity continuous the minimum is calculated using \( \textrm{min} = -\frac{1}{\beta} \log \sum_i \exp\left( -\beta s_i \right) \) The value of \(\beta\) in this function is specified using (BETA= \(\beta\)). The final value can be referenced using label.altmin. You can use multiple instances of this keyword i.e. ALT_MIN1, ALT_MIN2, ALT_MIN3... The corresponding values are then referenced using label.altmin-1, label.altmin-2, label.altmin-3... |

LOWEST | this flag allows you to recover the lowest of these variables. The final value can be referenced using label.lowest |

HIGHEST | this flag allows you to recover the highest of these variables. The final value can be referenced using label.highest |

SWITCH | This keyword is used if you want to employ an alternative to the continuous switching function defined above. The following provides information on the switchingfunction that are available. When this keyword is present you no longer need the NN, MM, D_0 and R_0 keywords. |