Moved gromacs module from mdevaluate to pygmx

pygmx/gromacs/logarithmic.pyx

@@ -0,0 +1,37 @@
+from libc.math cimport floor, ceil, fabs, log10
+
+def is_log_step(long long step, long long  per_decade):
+
+    # The first step will never be written
+    if step == 0:
+        return True
+
+    if step == 1:
+        return True
+
+
+    cdef double log_step = log10(step)
+    cdef double log_next = log10(step+1)
+    cdef double log_prev = log10(step-1)
+    cdef long long decade = int(log10(step))
+
+    # Idea: Is there a number x = decade + n / per_decade
+    # with 0 <= n < per_decade where
+    # | log_step - x | <= | log_prev - x |
+    # | log_step - x | <  | log_next - x |
+
+    # Calculate the closest numbers
+
+    cdef double n_smaller = floor((log_step - decade) * per_decade);
+    cdef double n_larger = ceil((log_step - decade) * per_decade);
+
+    cdef double prev_dist = fabs(log_prev-decade-n_smaller/per_decade);
+    cdef double dist_to_smaller = fabs(log_step-decade-n_smaller/per_decade);
+
+    cdef double next_dist = fabs(log_next-decade-n_larger/per_decade);
+    cdef double dist_to_larger = fabs(log_step-decade-n_larger/per_decade);
+
+    if dist_to_larger < next_dist or dist_to_smaller <= prev_dist:
+        return True
+    else:
+        return False