1
|
5883 Views
|
2 Replies
|
2 Total Likes
View groups...
Share
GROUPS:

# Docs say Units change physical displacement??

Posted 10 years ago
 Catastrophically wrong documentation?  tutorial/SymbolicCalculationsWithUnits under Integrate section.  There are 4 examples of "Calculate displacement over a given time.".  All 4 examples have the same physical integrand and limits, but differing units on the integration variable.  The results of 1st and 2nd example (250m) and the 3rd and 4th (25/6 m) are saying that the integrated displacement depends on the choice of units for the integration variable?????   That's dead wrong!!!  Or what am I missing (a brain)?Here is a cut/paste from the docs: Calculate displacement over a given time.  In[1]:= Integrate[Quantity[5, "Meters"/"Seconds"^2]*t, {t, Quantity[0, "Seconds"],    Quantity[10, "Seconds"]}]  Out[1]= Quantity[250, "Meters"]  In this form, the variable t is explicitly declared to be measured in seconds. In[2]:= Integrate[Quantity[5, "Meters"/"Seconds"^2]*t, {Quantity[t, "Seconds"],   Quantity[0, "Seconds"], Quantity[10, "Seconds"]}]Out[2]= Quantity[250, "Meters"]Here, the variable t is explicitly declared to be measured in minutes, and the endpoints are automatically converted to the correct units.In[3]:= Integrate[Quantity[5, "Meters"/"Seconds"^2]*t, {Quantity[t, "Minutes"],   Quantity[0, "Seconds"], Quantity[10, "Seconds"]}]Out[3]= Quantity[25/6, "Meters"]In[4]:= Integrate[Quantity[5, "Meters"/"Seconds"^2]*t, {Quantity[t, "Minutes"],   Quantity[0, "Minutes"], Quantity[1/6, "Minutes"]}]Out[4]= Quantity[25/6, "Meters"]Calculate displacement symbolically.In[5]:= Integrate[Quantity[a, "Meters"/"Seconds"^2]*t, {t, Quantity[ti, "Seconds"],   Quantity[tf, "Seconds"]}]Out[5]= Quantity[((a tf^2)/2 - (a ti^2)/2), "Meters"]
2 Replies
Sort By:
Posted 10 years ago
 Include the Quantity wrapper around t in the integrand.In[ ]:= Integrate[Quantity[5, "Meters"/"Seconds"^2]*Quantity[t, "Minutes"], {Quantity[t, "Minutes"], Quantity[0, "Seconds"], Quantity[10, "Seconds"]}]Out[ ]= Quantity[250, "Meters"]
Posted 10 years ago
 Thanks, Christopher, that is a helpful workaround.  Yet I'm still concerned that implementation of Quantity[], not to mention a portion of its documentation, is seriously flawed.  I've reported this to Wolfram Support.