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• physics.units
  • fixed numerical error in conversion of statcoulomb and coulomb (#24325 by @1e9abhi1e10 and @smichr)

This will be added to https://github.com/sympy/sympy/wiki/Release-Notes-for-1.12.

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#### References to other Issues or PRs
fixes #24319 ,#24381 ,#24281
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#### Brief description of what is fixed or changed
fixes numerical error in the conversion of `coulomb` and `statcoulomb` 




#### Other comments


#### Release Notes

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<!-- BEGIN RELEASE NOTES -->
* physics.units
     *  fixed numerical error in conversion of statcoulomb and coulomb

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Update

The release notes on the wiki have been updated.

Why it is showing an AssertionError, In my former PRs also faced the same issue. How can I fix it!

Why is it showing an AssertionError, In my former PRs also faced the same issue. How can I fix it!

When I am using try except statements it doesn't show any error, Can I use these statements?

Benchmark results from GitHub Actions

Lower numbers are good, higher numbers are bad. A ratio less than 1
means a speed up and greater than 1 means a slowdown. Green lines
beginning with + are slowdowns (the PR is slower then master or
master is slower than the previous release). Red lines beginning
with - are speedups.

Significantly changed benchmark results (PR vs master)

Significantly changed benchmark results (master vs previous release)

       before           after         ratio
     [41d90958]       [48018712]
     <sympy-1.11.1^0>                 
-     1.27±0.04ms         830±50μs     0.65  solve.TimeSparseSystem.time_linear_eq_to_matrix(10)
-     3.63±0.09ms      1.49±0.06ms     0.41  solve.TimeSparseSystem.time_linear_eq_to_matrix(20)
-      7.03±0.1ms      2.09±0.09ms     0.30  solve.TimeSparseSystem.time_linear_eq_to_matrix(30)

Full benchmark results can be found as artifacts in GitHub Actions
(click on checks at the top of the PR).

You get an AssertionError when an assert fails, so you can not use try-except here, because that means you're allowing a failed test. It's not surprising that the test fails, because you changed the test, without changing the underlying algorithm that obtains the test result.

You get an AssertionError when an assert fails, so you can not use try-except here, because that means you're allowing a failed test. It's not surprising that the test fails, because you changed the test, without changing the underlying algorithm that obtains the test result.

Okay Sir ,I will!

You get an AssertionError when an assert fails, so you can not use try-except here, because that means you're allowing a failed test. It's not surprising that the test fails, because you changed the test, without changing the underlying algorithm that obtains the test result.

I tried a lot but cannot able to fix the !assertion error. Can you pls guide me for moving ahead

I tried a lot but cannot able to fix the !assertion error. Can you pls guide me for moving ahead

The assertion error is obvious if you just change the tests without making corresponding changes in the code.
I checked the premise of this Pull Request and the expected output you show is indeed correct. The following git diff will correct the code and make your tests work (you will have to change some other tests related to statcoulomb too which I have shown below) -

--- a/sympy/physics/units/systems/cgs.py
+++ b/sympy/physics/units/systems/cgs.py
@@ -56,7 +56,7 @@
 cgs_gauss.set_quantity_scale_factor(maxwell, sqrt(centimeter**3*gram)/second)

 # SI units expressed in CGS-gaussian units:
-cgs_gauss.set_quantity_scale_factor(coulomb, speed_of_light*statcoulomb/10)
+cgs_gauss.set_quantity_scale_factor(coulomb, 10*speed_of_light*statcoulomb)

--- a/sympy/physics/units/tests/test_unit_system_cgs_gauss.py
+++ b/sympy/physics/units/tests/test_unit_system_cgs_gauss.py
@@ -11,10 +11,10 @@

 def test_conversion_to_from_si():

-    assert convert_to(statcoulomb, coulomb, cgs_gauss) == 5*coulomb/149896229
-    assert convert_to(coulomb, statcoulomb, cgs_gauss) == 149896229*statcoulomb/5
+    assert convert_to(statcoulomb, coulomb, cgs_gauss) == coulomb/2997924580
+    assert convert_to(coulomb, statcoulomb, cgs_gauss) == 2997924580*statcoulomb
     assert convert_to(statcoulomb, sqrt(gram*centimeter**3)/second, cgs_gauss) == centimeter**(S(3)/2)*sqrt(gram)/second
-    assert convert_to(coulomb, sqrt(gram*centimeter**3)/second, cgs_gauss) == 149896229*centimeter**(S(3)/2)*sqrt(gram)/(5*second)
+    assert convert_to(coulomb, sqrt(gram*centimeter**3)/second, cgs_gauss) == 2997924580*centimeter**(S(3)/2)*sqrt(gram)/second

     # SI units have an additional base unit, no conversion in case of electromagnetism:
     assert convert_to(coulomb, statcoulomb, SI) == coulomb
@@ -37,7 +37,7 @@ def test_cgs_gauss_convert_constants():
     assert convert_to(speed_of_light, centimeter/second, cgs_gauss) == 29979245800*centimeter/second

     assert convert_to(coulomb_constant, 1, cgs_gauss) == 1
-    assert convert_to(coulomb_constant, newton*meter**2/coulomb**2, cgs_gauss) == 22468879468420441*meter**2*newton/(25000000000*coulomb**2)
+    assert convert_to(coulomb_constant, newton*meter**2/coulomb**2, cgs_gauss) == 22468879468420441*meter**2*newton/(2500000*coulomb**2)

Ping @dyc3 for review. This pull request seems correct . Could you have a look if it is good to go in ?

I'm concerned with the lack of sources to justify this change, but if we are sure this is mathematically correct, then I'm good to merge this in.

This needs to have a release notes entry, please edit the PR description to add it.

Now it is fine ?
If something is wrong pls correct me .
Thank you!

I'm concerned with the lack of sources to justify this change, but if we are sure this is mathematically correct, then I'm good to merge this in.

The mathematical correctness of this change can be verified on wikipedia here in the relation between Statcoulomb and Coulomb section.

Yup, release notes look good, thank you!

I think this also resolves issue #24281. Could you check on your branch if the output is as desired. If yes, you should add "fixes # 24281" to the OP of the PR too.

I think this also resolves issue #24281. Could you check on your branch if the output is as desired. If yes, you should add "fixes # 24281" to the OP of the PR too.

cgs_gauss.set_quantity_scale_factor(coulomb, speed_of_light*statcoulomb/10)
cgs_gauss.set_quantity_scale_factor(ampere, speed_of_light*statcoulomb/second/10)
cgs_gauss.set_quantity_scale_factor(volt, speed_of_light*statvolt/10**6)
#cgs_gauss.set_quantity_scale_factor(weber, 10**8*maxwell)
#cgs_gauss.set_quantity_scale_factor(tesla, 10**4*gauss)
#cgs_gauss.set_quantity_scale_factor(debye, One/10**18*statcoulomb*centimeter)
#cgs_gauss.set_quantity_scale_factor(oersted, sqrt(gram/centimeter)/second)
cgs_gauss.set_quantity_scale_factor(ohm, 10**9/speed_of_light**2*second/centimeter)
cgs_gauss.set_quantity_scale_factor(farad, One/10**9*speed_of_light**2*centimeter)
cgs_gauss.set_quantity_scale_factor(henry, 10**9/speed_of_light**2/centimeter*second**2)

This changes should be required

cgs_gauss.set_quantity_scale_factor(coulomb, 10*speed_of_light*statcoulomb)
cgs_gauss.set_quantity_scale_factor(ampere,10*speed_of_light*statcoulomb/second)
cgs_gauss.set_quantity_scale_factor(volt, 10**6/speed_of_light*statvolt)
#cgs_gauss.set_quantity_scale_factor(weber, 10**8*maxwell)
#cgs_gauss.set_quantity_scale_factor(tesla, 10**4*gauss)
#cgs_gauss.set_quantity_scale_factor(debye, One/10**18*statcoulomb*centimeter)
#cgs_gauss.set_quantity_scale_factor(oersted, sqrt(gram/centimeter)/second)
cgs_gauss.set_quantity_scale_factor(ohm, 10**5/speed_of_light**2*second/centimeter)
cgs_gauss.set_quantity_scale_factor(farad, One/10**5*speed_of_light**2*centimeter)
cgs_gauss.set_quantity_scale_factor(henry, 10**5/speed_of_light**2/centimeter*second**2)

I need to add a commit that makes these changes.
Let me know if something is wrong.

@dyc3 pls review it!

Regarding V vs statVolt, chatGPT got it wrong, too - if this PR is right, though it gets the relationship between feet and inches right. So what is the definitive source that is being used to check this?

The volt is larger than the statvolt. The volt is the unit of electrical potential difference in the International System of Units (SI), which is the modern metric system of units. One volt is equal to 1 joule per coulomb.

The statvolt is the unit of electrical potential difference in the centimeter-gram-second (CGS) system of units. One statvolt is equal to 1 g^1/2 cm^1/2 s^-3/2.

There is a conversion factor between statvolts and volts, which is equal to about 299.792458 statvolts per volt. This means that to convert from statvolts to volts, you would multiply the number of statvolts by this conversion factor. For example, if you had 100 statvolts, this would be equal to about 29,979.2458 volts.

To summarize, the volt is larger than the statvolt. The volt is the unit of electrical potential difference in the SI system, while the statvolt is the unit of electrical potential difference in the CGS system. There is a conversion factor of about 299.792458 statvolts per volt, which can be used to convert between these two units.

Regarding V vs statVolt, chatGPT got it wrong, too - if this PR is right, though it gets the relationship between feet and inches right. So what is the definitive source that is being used to check this?

The volt is larger than the statvolt. The volt is the unit of electrical potential difference in the International System of Units (SI), which is the modern metric system of units. One volt is equal to 1 joule per coulomb.

The statvolt is the unit of electrical potential difference in the centimeter-gram-second (CGS) system of units. One statvolt is equal to 1 g^1/2 cm^1/2 s^-3/2.

There is a conversion factor between statvolts and volts, which is equal to about 299.792458 statvolts per volt. This means that to convert from statvolts to volts, you would multiply the number of statvolts by this conversion factor. For example, if you had 100 statvolts, this would be equal to about 29,979.2458 volts.

To summarize, the volt is larger than the statvolt. The volt is the unit of electrical potential difference in the SI system, while the statvolt is the unit of electrical potential difference in the CGS system. There is a conversion factor of about 299.792458 statvolts per volt, which can be used to convert between these two units.

As we know that 1 volt = 1 joule / 1 coulomb
and 1 statvolt = 1 erg / 1 statcoulomb
so we can write 1 volt = 10**7 erg / 2997924580 statcoulomb
then 1 volt = 0.003335640951981521*erg / statcoulomb
then 1 volt = 0.003335640951981521*statvolt
And in CGS base units 1 statvolt is equal to cm^1/2⋅g^1/2⋅s^(-1) Reference

Regarding V vs statVolt, chatGPT got it wrong, too - if this PR is right, though it gets the relationship between feet and inches right. So what is the definitive source that is being used to check this?

The volt is larger than the statvolt. The volt is the unit of electrical potential difference in the International System of Units (SI), which is the modern metric system of units. One volt is equal to 1 joule per coulomb.

The statvolt is the unit of electrical potential difference in the centimeter-gram-second (CGS) system of units. One statvolt is equal to 1 g^1/2 cm^1/2 s^-3/2.

There is a conversion factor between statvolts and volts, which is equal to about 299.792458 statvolts per volt. This means that to convert from statvolts to volts, you would multiply the number of statvolts by this conversion factor. For example, if you had 100 statvolts, this would be equal to about 29,979.2458 volts.

To summarize, the volt is larger than the statvolt. The volt is the unit of electrical potential difference in the SI system, while the statvolt is the unit of electrical potential difference in the CGS system. There is a conversion factor of about 299.792458 statvolts per volt, which can be used to convert between these two units.

The main thing is that statvolt is greater than volt