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robmio · 02-04-2022, 10:18 AM

Hi everyone, as I was preparing to program my HP PRIME for Cox's regression, I found myself solving this equation:

solve (x / (1-a ^ x) = b).

The real calculator gives no result: "[]", while the simulator solves the equation with the Lambert function: LambertW. However, the "LambertW (number)" command does not give any results.
Curious, right?

See the attachment.

toml_12953 · 02-04-2022, 10:36 AM

(02-04-2022 10:18 AM)robmio Wrote: Hi everyone, as I was preparing to program my HP PRIME for Cox's regression, I found myself solving this equation:

solve (x / (1-a ^ x) = b).

The real calculator gives no result: "[]", while the simulator solves the equation with the Lambert function: LambertW. However, the "LambertW (number)" command does not give any results.
Curious, right?

See the attachment.

Does your calculator have a LambertW function built in? Mine doesn't (2021 12 02)

robmio · 02-04-2022, 10:46 AM

(02-04-2022 10:36 AM)toml_12953 Wrote: Does your calculator have a LambertW function built in? Mine doesn't (2021 12 02)

Hi, toml_12953. The "physical" calculator does not solve the equation at all, but the emulator does: see the attachment for the version of the emulator I use (2021 10 01).

Didier Lachieze · 02-04-2022, 11:02 AM

(02-04-2022 10:46 AM)robmio Wrote: The "physical" calculator does not solve the equation at all, but the emulator does: see the attachment for the version of the emulator I use (2021 10 01).

The physical calculator with the latest 2021 12 02 firmware does return the same result as the emulator. However it appears that the LambertW function is either not implemented on the Prime or not accessible from the command line.

robmio · 02-04-2022, 11:36 AM

(02-04-2022 11:02 AM)Didier Lachieze Wrote:
(02-04-2022 10:46 AM)robmio Wrote: The "physical" calculator does not solve the equation at all, but the emulator does: see the attachment for the version of the emulator I use (2021 10 01).

The physical calculator with the latest 2021 12 02 firmware does return the same result as the emulator. However it appears that the LambertW function is either not implemented on the Prime or not accessible from the command line.

You're right, as long as "Use i" is unchecked in "Cas setting".