Jacob not showing expected result - 01 - Possible BugRep

[StuartBruff]

Whilst playing around with a Newton-Raphson solver for a simultaneous set of functions, I noted a disparity between the Mathcad 15 and Mathcad Prime 7 results for the Jacobian of one set of functions.  To eliminate the possibility of other parts of the worksheet contaminating the environment, I copied the function to a blank worksheet.   Unfortunately, I get the same results.   

Why is the derivative d/dξ for just cos(x₀) yet isn't when multiplied by x₀??

Mathcad 15 returns the result I expect.

1. Does this happen in Mathcad Prime 6 under the legacy symbolic engine?
2. Is there a valid reason why this MP7 behaviour occurs?
3. If so, should it?
4. If not, is it a bug?

Stuart

[Werner_E]

Guess you ran into Primes infamous autolabeling bug.

Check the labels of all xi and set them manually to "variable".

EDIT: No, autolabeling seems not to be the cause here even though I experienced strange effects in P6 when I retyped your expressions, then copied them, switches to the legacy engine, selected the symbolically evaluated regions and pressed F9. Can't explain the error message in the first one

When I copy the expressions AFTER having switched to the legacy engine, I get

[StuartBruff]

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@Werner_E wrote:

Guess you ran into Primes infamous autolabeling bug.

Check the labels of all xi and set them manually to "variable".

EDIT: No, autolabeling seems not to be the cause

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Yes, I thought of that when I first hit the problem (https://community.ptc.com/t5/PTC-Mathcad/Newton-Raphson-method/m-p/771992/highlight/true#M199247). However, it was way past my bedtime and I thought sleep deprivation was stopping me from seeing the obvious.  Maybe it wasn't ...

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EDIT: No, autolabeling seems not to be the cause here even though I experienced strange effects in P6 when I retyped your expressions, then copied them, switches to the legacy engine, selected the symbolically evaluated regions and pressed F9. Can't explain the error message in the first one

When I copy the expressions AFTER having switched to the legacy engine, I get

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Stuart

[Werner_E · Accepted solution]

Reason for not working when I simply evaluated the regions after switching to the legacy symbolic was that I also must evaluate the definition of G(x) from anew. Not sure why.

Here are some other observations - and yes, I'd call i a bug.

"New" symbolic:

Legacy symbolic

[StuartBruff]

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@Werner_E wrote:

Reason for not working when I simply evaluated the regions after switching to the legacy symbolic was that I also must evaluate the definition of G(x) from anew. Not sure why.

Here are some other observations - and yes, I'd call i a bug.

"New" symbolic:

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Good stuff, Werner.  Let us hope some kindly PTC/Subscription individual makes it known to the Symbolic team.

Stuart

[DJNewman]

I decided to be kind and I let them know by linking to this thread.