Merge pull request #19 from aselimov/ft--random-position-selector

Ft  random position selector

README.md

@@ -226,3 +226,22 @@ This command remeshes the atoms/elements within the group to the new element siz
 ```
 
 If this option is passed then all files are automatically overwritten without asking the user.
+
+## Position Specification
+
+Specifying positions in cacmb can be done through a variety of ways. Examples of each format is shown below.
+
+`val` - Where `val` is a number, then that value in Angstroms is used as the position. As an example, `11.1` would be read in as a position of 11.1 $\AA$.
+
+`-inf` - This specifies the lower box boundary in the specific dimension. The vector `-inf -inf -inf`  specifies the bottom corner of the simulation cell which also acts as the simulation cell origin. The vector `-inf 10 3` instead puts only the x position at the simulation cell origin.
+
+`inf` - Similar to `-inf` but references the upper boundary of the box in that dimension
+
+`inf-val` - Using a minus sign reduces the position from the **upper boundary** by `val`. `inf-10` would be at a distance of $10 \AA$ from the upper boundary in that dimension.
+
+`inf+val` - This increases the position from the **lower boundary**. `inf+10` would be a position $10\AA$ from the lower boundary within the cell.
+
+`inf*val` - This gives you a fractional position in the simulation cell. As an example `inf*0.5` gives you the center point of the simulation cell. 
+
+`rand` - Returns a random position that lies within the simulation cell.
+

src/main.f90

@@ -37,6 +37,7 @@ program main
     !Call initialization functions
     call lattice_init
     call box_init
+    call random_seed
     force_overwrite=.false.
 
     end_mode_arg = 0

src/subroutines.f90

@@ -178,6 +178,7 @@ module subroutines
         real(kind=dp), intent(out) :: pos !The output parsed position value
 
         integer :: iospara
+        real(kind=dp) :: rand
 
         iospara = 0
         if(trim(adjustl(pos_string)) == 'inf') then 
@@ -208,6 +209,10 @@ module subroutines
                 read(pos_string(1:index(pos_string,'*')-1), *, iostat=iospara) pos
             end if
             pos = (box_bd(2*i)-box_bd(2*i-1))*pos + box_bd(2*i-1)
+
+        else if (trim(adjustl(pos_string)) == 'rand') then 
+            call random_number(rand)
+            pos = (box_bd(2*i)-box_bd(2*i-1))*rand + box_bd(2*i-1)
         else
             read(pos_string, *, iostat=iospara) pos
         end if