Define function `get_ishape`

Convert_Matlab/convert_id.py

@@ -7,3 +7,13 @@ def days_1950(date_num):
     """
     date = datetime.date.fromordinal(date_num - 366) - datetime.date(1950, 1, 1)
     return date.days
+
+def get_ishape(d_init, ishape_last, days_1950, eddy_index):
+    k = days_1950 - d_init
+    
+    if k == 0:
+        ishape = eddy_index - 1
+    else:
+        ishape = ishape_last[k - 1] + eddy_index
+        
+    return ishape