 ``` Travel-Companion over the complex plane and along the imaginary axis This journey requires some knowledge about vectors and You should be able to add them, to multiply them with a scalar(number) and to build the dot-product - and so equipped You travel through an euclidian vector-space, as this the algebraic structure or the set of calculation rules is called. And You can do this in as many mathematical or physical dimensions as You like -of course there are not more than three of space in it. Here we restrict ourselves to just 2D, to a plane. There are lots of reports about a "complex plane" or an "imaginary axis" - just translate it into "2D-plane" and "y-axis". I can assure You, that there is no mathematical difference between these.You can write one and the same vector in the form of coordinates as well as an expression of two basis vectors =1 and =i as a+i*b (the first form is called ordered pairs of real numbers, the second form linear combination of the basis elements). In physics they use j instead of i for the vector A computer makes no difference, do You have to? See my calculator For a beginner it was always very hard to grasp the difference - as there is none. And for all of those, who had to learn to do this brain-twist, it is even harder to disentangle their thoughts, but it is necessary, as You will see. Once You got this, there's just one more difference to look at : the multiplication. It is defined as (a+i*b)*(u+i*v)=(a*u-b*v)+u*(a*v+b*u) or according to i*i=-1 and in coordinate-form * = Geometrically it means an addition of differences of direction and a multiplication of length. This is an extension of the multiplication of real numbers, of 1D and it's different from the r.s.m. the multiplication of a vector by a real number and different from the dot-multiplication. And this multiplication is only possible in 2D. Again there is no justification, not even a historical one, to have a special "complex" world with this multiplication besides the normal 2D-vectors. It's not worth to speculate, why some like it so complicated. This multiplication is included in the euclidian space, as you can build this product by r.s.m., the addition and dot. Just as you can build with these three let's say the subtraction or the metric(the distance between two points on the plane or in other words the length of the movement from the tip of one arrow to the tip of another,if they are tailed together). Now You can start on Your journey. In electronics You can learn to calculate circuits.Look for vibrations of ac-currents in a pointer-diagramm and You will find this in two forms, one without "complex-numbers"and one with them. The second one is easier, as here the multiplication is used. Compare both methods and see for Yourself: the pointer is pointing in the same directions, what is called the i-axis in one form is named y-axis in the other. What is true for constant vectors will show up again, when You look at variables and functions.The most general form (of termdefined functions) in 2D one can build is by means of 1D, just R: calculate from two independent variables x and y two functions u(x,y) and v(x,y), that is building two terms in R using x and y. Associate x and y with the two coordinates of the domain and let u and v do the same in the range.In this mathematical area you can find lot of useful material. What some might be unaware of is, that the functions of "complex variables" are part of this and what is said about the first, is true for the second. And You can write the function also in the form f(x+i*y)=u(x,y)+i*v(x,y). Only for those who learned a bit about calculus: The extension of differentiation into 2D is the partial differentiation, that is: or delta u/delta y= is differentiating u for y in the way You learned, but treating the other variable x like any constant or number. You can get four terms and they are arranged in a matrix the functionalmatrix, that is or This is valid for both kind of functions. Now comes the tricky part: We restrict ourselves to the operations + and * and everything we can build with it, like the division. We will have no longer the dot, or the metric. We cant even go to polar coordinates.You might use a coordinate system, but even this is not essential. I just stick to the only definition of complex numbers one can find in literature. An important geometric conclusion is, that you cannot change orientation. The restriction to (R2,+,*) is not always followed in literature and that's why i proposed the name Bombelli instead of "C, the commutative field of complex numbers". (R2,+,*) is a commutative field, it's algebraic complete (that is: every polynomial has as many zeroes (roots), as its degree). The same algebraic structure You get, when You look at some 2x2-matrices with their addition, their r.s.m. and their multiplication - restrict Yourself here to the matrices of this form They have exactly the same possibilities:translations, rotations with shrinking/stretching. Advance to variables. You must recognize, that here You cannot calculate the components of the independent variable differently, let's say x˛+3y as with the euclidian vectors. Build a term with x in R and replace x by z, or sligthly more expanded: build a term in 2D, but only use one independent variable z (instead of two independent variables, each of one dimension) - and only after this replace z by or by a+i*b and calculate until You get two functions u(a,b) and v(a,b) combined into 2D as =u+i*v. It's the general form of any possible function here, build as a term in (R2,+,*) and using just z, - it's called holomorphic function, as You leave the variable whole, unsplit. Nearly every formula You know already about functions of R1, which are termdefined You can directly transfer to these special 2D-functions (=in Bombelli termdefined). If You like flow charts: the angles and their orientation of any grid in the domain will be transferred by any such function exactly without change into the range (strict comform mapping). With vector fields.... ... ....lot's of results can be reached. Only for those who learned a bit about calculus: The functionalmatrix of these functions always takes the form or (Cauchy-Riemann equations) And as mentioned above, the matrices of this form are isomoph to 2D-vectors: every matrix of this form can be replaced by = So the derivates of the holomorphic functions are 2D also! When You travel in the domain, the trace You leave will be transferred to the range by the termdefined function. Is this a holomorphic function, then the derivate is independent of direction, that means the change of traveldirection is only dependend on the point, You travel through, but not on the way, You are going. Have fun on Your trips around ```