Multiplying two complex numbers
complex-turn is one function. Everything below came out of it during this
build, at parameters taken from the essays rather than invented for this page — so a figure
here is the same figure a reader meets in an essay, and if the generator changes, this page
changes with it.
With nothing chosen
The image of four circles, turning 0 to 3 times
Powers of a complex number
The 5 5th roots of unity
3 roots, and the circles that enclose them
The powers of 4 roots, added: 1, −1, 4, −5
What it checks while it draws
Collected by running the family and recording what it asserted, not written here. The count is how many separate times the claim was put to the test while these drawings were made.
- the composite 4 does not divide P(4) ×17737
- the prime 2 divides P(2) ×2262
- at n = 0, 3 times the class-0 total less 2ⁿ is what the other roots contribute ×98
- (3 + 4i)^1 is not a real number ×60
- and it has length 5^1 ×60
- the search for 6 agrees with the prime-factor rule at 1 terms ×47
- the coefficient of x^0 at power 1 ×40
- P(0) − ρ^0 is twice the real part of σ^0 ×31
- the derivative of z^3 − 1 is 3z^2: coefficient 0 vanishes ×27
- the root at step 0 first returns to 1 after 1 multiplications ×26
- root 0 raised to the 5 is 1 ×24
- the coefficient of x^0 in the product is the one in xⁿ − 1 ×16
- and that number is the Möbius function of 1 ×12
- and the average over the 1th roots of ∏(1 + ζᵏ) gives the same ×12
- the count is the necklace count exactly when 1 is odd ×12
- the odd-divisor sum for 1 is a multiple of 1 ×12
- the primitive roots of order 1 add to a real number ×12
- the subsets of 1…1 with a total divisible by 1, listed, match the formula ×12
- the product 1,4,6,4,1 was found by the search ×10
- row 1: the terms written out add to the entry ×8
- the factor belonging to the roots of order 1 has degree φ(1) ×8
- the gaps at n = 6 repeat those at n = 0 ×8
- the product 1,-1,-1,1 was found by the search ×8
- the real part of (3 + 4i)^1 is not a multiple of 5, so the fraction is in lowest terms ×8
- 1 + ζ^0 has length 2|cos(0π/3)| ×7
- and it is the coefficients of index 0 mod 3 added one by one ×7
- the curve the image of the circle of radius 0.4 never passes exactly through the origin ×7
- the image of radius 0.4 turns once for each root inside it ×7
- the image of the circle of radius 0.4 closes up after a whole number of turns ×7
- the product 1,2,1 was found by the search ×7
- the walk along the image of the circle of radius 0.4 is fine enough to see which way it turned ×7
- the share is exactly 1/2 precisely when the die's polynomial vanishes at the other roots ×6
- the throws with a total divisible by 2, counted through the roots ×6
- the roots of the 1-th derivative lie in the hull of the ones before ×5
- at degree 4 nothing sits between measure 1 and the smallest found ×4
- exactly one root of p′ between the 1-th and 2-th roots ×4
- the circle of radius 0.4 has 0 roots inside and turns 0 times ×4
- the class-0 total found through the roots is real ×4
- the curve the image of radius 0.4 never passes exactly through the origin ×4
- the degree-1 cyclotomic products, multiplied out, are exactly the polynomials found ×4
- the image of radius 0.4 closes up after a whole number of turns ×4
- the walk along the image of radius 0.4 is fine enough to see which way it turned ×4
- x-polynomial x⁴ + 2x³ + 2x² + 2x + 1 has every root in the disc and is a product of cyclotomic polynomials ×4
- x-polynomial x⁴ − 4x³ + 6x² − 4x + 1 has every root in the disc and is a product of cyclotomic polynomials ×4
- side 1 stays outside the ellipse and touches it at its midpoint (equilateral) ×3
- side 1 stays outside the ellipse and touches it at its midpoint (obtuse) ×3
- side 1 stays outside the ellipse and touches it at its midpoint (scalene) ×3
- the product -1,-1,1,1 was found by the search ×3
- the product -1,3,-3,1 was found by the search ×3
- far out, the image turns once for each power of z, which is 3 times ×2
- the product -1,0,1 was found by the search ×2
- the product -1,2,0,-2,1 was found by the search ×2
- the product 1,-2,1 was found by the search ×2
- the product 1,0,-2,0,1 was found by the search ×2
- the roots agree on p₁ at c = -3 ×2
- the roots agree on p₁ at c = 1 ×2
- the roots agree on p₂ at c = -3 ×2
- the roots agree on p₂ at c = 1 ×2
- the roots agree on p₃ at c = -3 ×2
- the roots agree on p₃ at c = 1 ×2
- x-polynomial x³ + 2x² + 2x + 1 has every root in the disc and is a product of cyclotomic polynomials ×2
- x-polynomial x³ − 3x² + 3x − 1 has every root in the disc and is a product of cyclotomic polynomials ×2
- 271441 is 521 squared ×1
- a polynomial of degree 3 has 3 roots ×1
- all 12 roots add to zero ×1
- and |σ|²ρ = 1, the constant term ×1
- and close in it does not go round the origin at all ×1
- and has no imaginary part left ×1
- and it crosses between them ×1
- and it divides its own Perrin number ×1
- and its coefficients are whole numbers ×1
- and its measure is 1.17628 ×1
- and mod 4 it does outgrow anything mod 3 allows ×1
- and multiply to the constant term, with a sign that follows the degree ×1
- and one inside, its reciprocal ×1
- and so is the necklace sum ×1
- and the angles add ×1
- and the degrees of the factors add to n, because every root has exactly one order ×1
- and the derivative's roots have the same average as the roots ×1
- and the middle coefficient lies strictly between −2 and 2 ×1
- and the two off the circle multiply to 1 ×1
- and their imaginary parts cancel ×1
- and their imaginary parts cancel, because the coefficients are real ×1
- and whole ones ×1
- and Σz³ is −3c ×1
- at a place where the discriminant is passing through zero ×1
- at most eight powers are labelled ×1
- between 1 and 8 dice are thrown ×1
- between 2 and 8 moduli from 2 to 12 are compared ×1
- between 20 and 300 polynomials a degree ×1
- between 8 and 400 powers are drawn ×1
- between two and five whole-number constant terms ×1
- between two and six powers are chained ×1
- each example lands in the group it was chosen for ×1
- each hull is no larger than the one before ×1
- each pairing's value is a root of the resolvent cubic, computed from the coefficients alone ×1
- each root found really is a root ×1
- each step of the division gives a whole number ×1
- eight of its ten roots are on the unit circle ×1
- every root found is a root of unity ×1
- every root found really is a root ×1
- every root is on the unit circle ×1
- every root of p′ is real ×1
- every root of p′ lies in the hull of the roots (cluster) ×1
- every root of p′ lies in the hull of the roots (line) ×1
- every root of p′ lies in the hull of the roots (scatter) ×1
- in both coordinates ×1
- Lehmer's polynomial has four roots on the upper half of the circle ×1
- mod 3 no class is ever more than 2/3 away from a third of 2ⁿ ×1
- mod 4 the gap is no larger than what 1 + i and 1 − i can contribute ×1
- no power of (3 + 4i)/5 up to the 60th returns to 1 ×1
- no power of a root of Lehmer's polynomial up to the 80th returns to 1 ×1
- no sampled root is as far as 1 from every root of the derivative ×1
- one fewer root of p′ than of p ×1
- one is outside ×1
- one real root and a complex pair ×1
- one to three of the named root sets ×1
- one to three of the named triangles ×1
- outside the hull the pushes never cancel ×1
- quartic is read only by the pairings view ×1
- row 1: the identity and the roots agree on p₁ ×1
- row 2: the identity and the roots agree on p₂ ×1
- row 3: the identity and the roots agree on p₃ ×1
- row 4: the identity and the roots agree on p₄ ×1
- row 5: the identity and the roots agree on p₅ ×1
- row 6: the identity and the roots agree on p₆ ×1
- row 7: the identity and the roots agree on p₇ ×1
- row 8: the identity and the roots agree on p₈ ×1
- set is read only by the vanish view ×1
- six roots, then five, four, three, two and one ×1
- subsets are listed for sets of at most 14 numbers ×1
- the 1-th powers of the roots add to p₁, found from the coefficients alone ×1
- the 2-th powers of the roots add to p₂, found from the coefficients alone ×1
- the 24 permutations fall into 6 classes of 4 by their effect on the pairings ×1
- the 3-th powers of the roots add to p₃, found from the coefficients alone ×1
- the 4-th powers of the roots add to p₄, found from the coefficients alone ×1
- the bar chart shows a set of 3 to 9 numbers inside the table ×1
- the classes are remainders mod 3 or mod 4 ×1
- the classes are remainders on division by 2 to 6 ×1
- the classes between them hold all 2ⁿ of the coefficients' total ×1
- the complex pair lies inside the unit circle ×1
- the derivative of a degree-5 polynomial has 4 roots ×1
- the distances to the two roots of p′ add to the same total at every midpoint (equilateral) ×1
- the distances to the two roots of p′ add to the same total at every midpoint (obtuse) ×1
- the distances to the two roots of p′ add to the same total at every midpoint (scalene) ×1
- the division leaves no remainder ×1
- the ellipse is centred on the centroid ×1
- the equation is zⁿ = 1 for n between 4 and 20 ×1
- the factors multiply out to a polynomial of the right degree ×1
- the family passes from three real roots to one ×1
- the fifth derivative's one root is the average of the six ×1
- the fifth-root polynomial has real coefficients ×1
- the grid runs to between 21 and 81 ×1
- the lengths multiply ×1
- the loops sit inside their panel, below its header ×1
- the modulus is small enough for exact products in a double ×1
- the nearest polynomial outside the disc is well clear of the tolerance ×1
- the number of powers drawn is between 2 and 24 ×1
- the number of powers taken is between 1 and 24 ×1
- the number of roots of unity is between 2 and 24 ×1
- the one outside is real ×1
- the pairings that come out whole are the resolvent's rational roots ×1
- the permutations fixing every pairing are the identity and the three double swaps ×1
- the point drawn is a root of Lehmer's polynomial ×1
- the point is on the unit circle ×1
- the point whose powers are drawn is one the family names ×1
- the polygon drawn has between 3 and 16 corners ×1
- the polygon has 5 to 16 sides ×1
- the polynomial has a degree ×1
- the polynomial has a degree between 1 and 6 ×1
- the polynomial is monic, so its power sums are whole numbers ×1
- the polynomials searched have degree 2 to 4 ×1
- the power drawn is between 2 and 16 ×1
- the power sum is still an exact whole number ×1
- the product -1,0,0,0,1 was found by the search ×1
- the product -1,1 was found by the search ×1
- the product 1,1 was found by the search ×1
- the pushes cancel at each root of p′ ×1
- the quartic has no whole-number root, so its pairings are not trivially rational ×1
- the quartic is one the family names ×1
- the radii drawn are between 2 and 5 positive numbers no larger than 4 ×1
- the real root is the plastic number, 1.3247… ×1
- the remainders are taken on division by 2 to 12 ×1
- the ring outside the hull was checked ×1
- the root set is one the family names ×1
- the roots add to minus the next coefficient over the leading one ×1
- the roots are distinct ×1
- the roots sum to zero ×1
- the search stays small enough to finish ×1
- the sequence is drawn to between 12 and 40 terms ×1
- the sequence settles on the nearest whole number to ρⁿ well inside the range ×1
- the seven-term sum splits into turned regular polygons ×1
- the seventh root returns to 1 at the seventh power ×1
- the sign of the discriminant says how many roots are real ×1
- the six-term sum is minimal and is no union of turned polygons ×1
- the smallest measure at degree 10 is Lehmer's polynomial ×1
- the sum is one the family names ×1
- the sum is zero, exactly, modulo the cyclotomic polynomial ×1
- the sums take all three of the values that function takes ×1
- the sweep meets both cases ×1
- the sweep takes between 20 and 800 samples ×1
- the swept family is a depressed cubic with a negative linear term ×1
- the table of sums runs to between 6 and 16 ×1
- the table runs to at most 12 powers ×1
- the table runs to between 3 and 10 powers ×1
- the table runs to between 6 and 16 ×1
- the third derivative's three roots still span a triangle ×1
- the totals account for every throw ×1
- the two chains drawn are for moduli in the table ×1
- the vanish view takes its n from the named sum ×1
- the view is one the family draws ×1
- three to seven real roots ×1
- with an even number of sides some diagonals meet three or more at a point ×1
- with an odd number of sides no three diagonals meet, so there are C(n, 4) crossing points ×1
- with nothing imaginary left over ×1
- x-polynomial x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x − 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x² + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x² + 2x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x² + x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x² − 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x² − 2x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x² − x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x³ + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x³ + x² + x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x³ + x² − x − 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x³ − 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x³ − x² + x − 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x³ − x² − x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ + 2x² + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ + 2x³ − 2x − 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ + x² + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ + x³ + 2x² + x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ + x³ + x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ + x³ + x² + x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ + x³ − x − 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ − 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ − 2x² + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ − 2x³ + 2x − 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ − x² + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ − x³ + 2x² − x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ − x³ + x − 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ − x³ + x² − x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- x-polynomial x⁴ − x³ − x + 1 has every root in the disc and is a product of cyclotomic polynomials ×1
- Σz is 0 for every member ×1
- Σz² is 6 for every member ×1
Where it is called
Every figure on this list is drawn by the same rule, so a change to the rule changes all of them at once. That is why the list is published.
A loop that cannot miss the middle
Feed a circle into a polynomial and a closed loop comes out. A small circle gives a loop that does not enclose the origin; a large one gives a loop that goes round it as many times as the degree. Something has to happen in between, and that something is a root.
AlgebraA multiplication that remembers the order
Four characters — i² = j² = k² = ijk = −1 — define a multiplication in which ab and ba are different numbers. Everything follows from them, including the fact that a rotation of a solid body has two names, and that two full turns are needed to get one of them home.
AlgebraEvery power sum, from the coefficients alone
Raise the roots of a polynomial to the k-th power and add them. However the roots turn, the total is a whole number when the coefficients are, and Newton's identities produce it from the coefficients one step at a time — no root is ever found. Run the rule on x³ − x − 1 and out comes Perrin's sequence, whose terms know which numbers are prime, nearly.
AlgebraEvery third coefficient
Add every third number in the twelfth row of Pascal's triangle and the answer is 1366 — a third of 4096, rounded up. Which way the rounding goes is decided by two arrows of length one in the complex plane, and the same average over the roots of unity counts dice totals, subsets and necklaces.
AlgebraMultiplying is turning
Complex numbers are introduced as an algebraic dodge for square roots of negatives. They are better understood as the arithmetic of rotation, at which point every rule stops needing to be remembered.
AlgebraOn the circle and never home
Every root of unity lies on the unit circle, and so does the point (3 + 4i)/5 — yet no power of it ever returns to 1. A root of a whole-number polynomial of degree ten does the same. What forces a point home is a condition on the numbers its polynomial ties it to, and how far one of them may stray is a question open since 1933.
AlgebraThe lattice that runs the other way
The symmetries of a polynomial's roots form a group, and the fields between the bottom and the top form a lattice. The two are the same picture, one of them turned over — a bigger group of symmetries fixes less, so it names a smaller field.
AlgebraThe polygon an equation forces
The n solutions of z to the n equals one are the corners of a regular polygon, and nearly everything about them — that they form a group, that they sum to zero, that the equation factors into pieces with whole-number coefficients — is that picture read carefully.
AlgebraThe roots of the slope stay inside
Mark the roots of a polynomial in the complex plane and stretch a band around them. However the roots are arranged, the roots of the derivative land inside the band — never outside, never on a new frontier. The reason is a balance of pushes, the same reason makes the derivative of a cubic mark the foci of an ellipse nobody asked for, and a question about how far inside the roots must sit has been open since 1958.
AlgebraThe sums of roots of unity that add to nothing
All n of the n-th roots of unity add to zero, and so does any regular polygon among them, turned. Those are not the only vanishing sums: six thirtieths of a turn close into a loop with no polygon in them. Which counts of roots can close at all is decided by the prime factors of n — no seven fifteenths ever add to zero — and the same question counts where the diagonals of a regular polygon cross.
AlgebraThree ways to pair four roots
Four roots can be split into two pairs in exactly three ways, and the three numbers r·r′ + r″·r‴ those pairings give are the roots of a cubic whose coefficients can be read straight off the quartic. That cubic is where Ferrari's formula gets its cube roots, and it is also a verdict: whether its roots are rational decides which of the twenty-four symmetries the quartic's roots actually have.
AlgebraWhat the coefficients already know
Finding the roots of a polynomial is hard and often impossible in closed form. Reading off their sum, their product and how many of them are real is none of those things — those numbers are sitting in the coefficients, and no root-finding is required to get at them.
AnalysisWhen the period grows without bound
A repeating signal has a spectrum of separate lines. Stretch the gap between repeats and the lines crowd together while the curve they sit on stays exactly where it is — and at infinite period the lines are gone and the curve is the whole answer.