Release 0.9.20 "Corpus" - Polynomials and algebraic expressions

This release focuses on support for polynomial, root finding and algebraic expressions, and on making evaluation of algebraic expressions behave closer to algebraic mode on the HP50G, i.e. treat ' like the HP50G treats a backquote expression or an expression entered in algebraic mode.

New features

• LU command generating LU-decomposition for matrices
• REF, RREF and RREFP commands to put matrices in Echelon form
• Order command to reorder variables in the current directory
• PEval, PRoot and Zeros commands for polynomials and expressions
• Unique and QuickUnique commands to keep unique values in a list
• DEPND and INDEP commands to set dependent/independent variables
• Implicitly recognize xlib and constants by name, e.g. c or Dedicace
• Flags to control the above, AutomaticConstants and AutomaticXLibs
• Preserve symbol case for existing variables
• Creating symbols matching builtin names using the Ⓥ prefix, e.g. ⓋHelp
• Value comparison for Sort or Unique now works with expressions
• Simplification now factors common ratios, e.g. A*X+B*X
• Primitive and derivative of a polynomial
• Several new constants lifted from the R47 constant catalog
• Hyperbolic secant functions sech,csch, coth, and their inverse
• CrDir can now take a list as input to create multiple directories

Bug fixes

• Crash in solver in case of error evaluating some intermediate step
• Correctly put parentheses in 'sin(x+1)' rendered in text mode
• Occasional object_error in as_text() on simulator
• Crash in IFT / IFTE if given invalid input
• Detection of expression vs. RPL programs during evaluation
• Crash in quotient or decimal conversions given erroneous input
• Parsing of 0+ⅈ, was incorrectly parsed as 0ⅈ
• Negating 0 no longer shows -0
• No longer allow incorrect mixing of ranges and uncertain numbers
• Dividing a polynomial by a number now divides constant terms
• Correctly split expressions that contain a single term when testing equations
• Fix simulator race condition while loading the keymap
• STO will no longer overwrite a directory with a non-directory value
• Purge will no longer erase non-empty directories, PGDir is now needed
• RAr constant uncertainty was incorrectly set to 0
• Swap keyboard legacy and 42k keymaps in simulator

Improvements

• Purely imaginary values such as 0+3ⅈ now render as 3ⅈ
• The LNAME command now returns a list in algebraic expressions
• Σ, ∏, ∂ and ∫, COMB and PERM now partially evaluate as on HP50G
• Refactor detection of symbolic arguments in functions for scalability
• Refactor detection of algebraic functions for scalability
• Signal when ui_refresh() takes too long due to internal race condition
• Do not drop input in multisolver when a wrong value is given
• Quick exit when parsing empty commands
• Rounding for →ℚ more accurately respects displayed precision
• Internal factoring with square roots and fractions to_sqrt, used in PRoot
• Internal integer and fraction square root, used in simplification
• Reorganize the polynomials menu to bring useful functions at first level
• Accept polynomials and tagged expressions in plotting commands
• Do not default imaginary part to 1 in complex::make (was error prone)
• Optimize the integer power case for range objects
• Zero detection for expressions and polynomials in simplifications
• Makefiles no longer emit confusing mv output in make compare
• New stack_buffer facility in the runtime to keep multiple exansions on stack
• Add ISOL tests for sec, csc, cot functions
• Consolidate project guidance into AGENTS.md
• Simplify simulator beep control logic: -N blocks beeps, -n restores them
• Refresh implementation status
• Update documentation for PGDIR, STO and RCL new capabilties
• Internal facility to swap arbitrary stack levels
• Update man page
• Add recorder_scope-compatible instrumentation for GC and available memory
• Accelerate display of constants/equations/library menus