IMSUM Function (Gnumeric)

IMSUM adds complex numbers: real components sum separately from imaginary components. It is useful for series impedances (where adding impedances is appropriate), vector/phasor addition, and signal components written as complex numbers. It is not ordinary SUM over a numeric-only column and must not be substituted for addition of quantities in incompatible units.

Version-specific error distinction: The online 1.12 manual describes malformed complex inputs as #VALUE!. The official 1.12.62 source instead returns #NUM! when parsing a malformed complex string; other unsupported value types can still return #VALUE!. Any #VALUE! expectations below are the manual’s older documented rule, not verified 1.12.62 output. No native error test was performed.

Official syntax and arguments

=IMSUM(z1,z2,…)

z1 and z2 are complex-number values or expressions. Further complex arguments may be supplied; the 1.12 manual displays an ellipsis. Its synopsis illustrates two inputs, but this is not evidence of a two-argument minimum: the 1.12.62 implementation uses a variable-argument iterator without enforcing that minimum in the callback. Arguments are written in the supplied order, although mathematical addition is commutative. Use Gnumeric’s COMPLEX(real,imaginary) helper to build unambiguous complex inputs. The manual specifically states that an invalid complex argument returns #VALUE!. Do not assume blanks, text ranges, and array coercion behave like another spreadsheet without native testing.

Reproducible worksheet

Independent arithmetic: (2+3i)+(1−2i)=(2+1)+(3−2)i=3+i. The exact way Gnumeric displays an imaginary coefficient of 1 may vary; treat 3+i and 3+1i as mathematically equivalent, not two separately observed outputs.

Direct and multi-input examples

• =IMSUM("2+3i","1-2i") → mathematically 3+i.
• =IMSUM("1+i","2-3i","-3+2i") → mathematically 0+0i. The visual representation of zero is not verified.
• =IMSUM(COMPLEX(3,4),COMPLEX(-1,-4)) → mathematically 2+0i.

Advanced application: a series impedance check

If C2 represents an inductor’s impedance 2+3i ohms and C3 represents another series component 1−2i ohms, =IMSUM(C2,C3) gives combined impedance 3+i ohms. In separate cells use =IMREAL(D2) and =IMAGINARY(D2) to audit the two components. Only series impedances add this way; parallel impedance needs the reciprocal/quotient relationship and is not computed with IMSUM alone.

Troubleshooting and limits

Compatibility

The Gnumeric manual labels IMSUM Excel-compatible. This is an upstream documentation label, not proof of identical array, blank, error, locale, j-suffix, or file round-trip behavior. The September 2026 release notes mention compatibility improvements for complex functions generally; compare actual installations for high-stakes migrations.

These examples are independently calculated expectations, not observed output from a running Gnumeric installation. The published Gnumeric 1.12 manual documents the function’s signature and relevant error behavior, and the Gnumeric project’s function catalogue records upstream implementation and test classifications. The official 1.12.62 release announcement confirms that release exists (September 2026). The live manual/catalogue are not immutable 1.12.62 source-code snapshots, so document coverage must not be confused with runtime verification of every locale, platform, or build.

The examples use the English function names and the comma separators shown in the official manual. Your localized Gnumeric configuration might use another argument separator or decimal notation; use its Function Browser to confirm the accepted local entry format. Complex-number strings in the examples use the i suffix consistently. The Gnumeric manual also documents COMPLEX’s j suffix option, but do not mix conventions in one calculation without validating that workflow in your installation. Gnumeric is generally distributed through Linux/Unix-like systems and source packages; the project does not provide current official Windows binaries.

• COMPLEX — construct consistent a+bi input strings from coefficients.

• IMREAL — extract the real coefficient.

• IMAGINARY — extract the imaginary coefficient.

• IMPRODUCT — multiply complex values.

• IMABS — calculate the modulus.

• IMPOWER — raise a complex value to a power.

1. Gnumeric Manual 1.12 — Complex functions: documented purpose, signature, argument meanings, #VALUE! notes, Excel-compatibility label and cross-references for IMSUM. Dynamic 1.12-series documentation, not a pinned release source tree.
2. Official Gnumeric function catalogue: imsum listed as Complete implementation with Basic upstream test classification; that describes upstream project metadata, not execution of this worksheet. The live catalogue currently presents an aggregate count that differs from the 1.12.62 release registry, so it is not used to assert catalogue completeness.
3. Gnumeric 1.12.62 official release announcement: release existence and Excel/complex-function compatibility work (the release announcement does not guarantee each example or Excel round-trip).
4. GNOME official 1.12 source-release directory: official versioned source distribution; the official 1.12.62 source was inspected for this review.

Evidence categories: official-manual documentation checks; official-catalogue metadata checks; independent arithmetic checks. Not performed: native function execution, locale-specific execution, Excel comparisons, GUI screenshots, or application screenshots.