Questions about MATLAB, questions about matlab.

You don't need to learn MATLAB, you can go to university and learn it again.

MATLAB is just a tool for numerical calculations, and if you learn it now, you're going to ignore some of the principles of the formulas, and you won't be able to learn the basics.

It's like if you don't understand the principles of addition, subtraction, multiplication and division, and start using a calculator, it will only cause a decrease in your independent calculation ability.

MATLAB is a commercial software, which belongs to the numerical calculation class according to the classification of mathematical software functions.

MATLAB has powerful mathematical calculation capabilities, mainly involving all aspects of advanced mathematics.

Because of the comprehensive and powerful functions of MATLAB, many American colleges and universities require graduate students to master it when they enter the school.

Therefore, it is not recommended to learn MATLAB too early. It's not easy for undergraduates to do MATLAB either. Junior high school students should focus on the learning of basic knowledge.

In addition, the pressure of the high school entrance examination is also relatively high, so it is not recommended to spend too much time on MATLAB. If you are interested, you can use your spare time. Don't give up on what you need.

You can't use this without a good matrix concept.

If you want a powerful calculator, try Maple, or Mathimatics, where the math concepts are more natural than MATLAB.

There's so much math involved in MATLAB. It's too early to learn in the first year of junior high school. Let's learn C or other languages.

It's too early to learn. There is a need for a foundation in MATLAB. First of all, you must have a foundation in mathematical theory, but also a foundation in programming (such as C language programs).

The idea of functions is very important, and trigonometric functions are an important member of the function family. If you understand the function, you will understand it all. Matrix is to first learn "Linear Algebra", the university course engineering mathematics.

That's one of the foundations of MATLAB. It can be seen from his name. MATLAB (Matrix Laboratory).

Let's study hard!!

If you learn the theory first, you will be able to study in college

The coefficients you are talking about should be the Fourier coefficients, which are the coefficients with constant properties of each periodic trigonometric function after the Fourier series of a function is obtained by the method of Fourier series.

You can refer to. FFT, on the other hand, is a fast Fourier transform and does not have coefficients.

Fast Fourier transform (FFT) is a fast algorithm for discrete Fourier transform, which is obtained by improving the algorithm of discrete Fourier transform according to the characteristics of discrete Fourier transform, such as odd, even, imaginary and real. It has made no new discoveries in the theory of the Fourier transform, but it can be said to be a big step forward in the application of discrete Fourier transforms in computer systems or digital systems.

A finite-long sequence can also be discretized in the frequency domain by a discrete Fourier transform (DFT).

Fast Fourier transform.

into finite length sequences. However, it is too computationally intensive to deal with the problem in real time, so the Fast Fourier Transform (FFT) is introducedIn 1965, Cooley and Tukey proposed a fast algorithm for calculating the Discrete Fourier Transform (DFT), reducing the computational amount of DFT by several orders of magnitude.

Since then, the research on Fast Fourier Transform (FFT) algorithms has been deepened, and the emerging discipline of digital signal processing has also developed rapidly with the emergence and development of FFT. According to the different methods of sequence decomposition and selection, a variety of FFT algorithms have been produced, and the basic algorithms are base 2DIT and basis also have important applications in discrete inverse Fourier transform, linear convolution and linear correlation.

help fft

Then take a look at it.

Theoretically, the 3 openings of -8 have 3 roots, i.e.: +2. All three roots can be obtained, x 3 + 8 = 0 (that is, x 3 = -8).

In MATLAB, you enter the following equation:

syms x

solve('x^3+8',x)

If you calculate it directly, only the first value is returned, and MATLAB does not have a function that directly opens the cubic dimension, it is calculated in the complex number field, and it is arranged according to the principal value of the radiator angle, so the last two values are not returned.

in the first formula'

It's the meaning of transpose, which is actually to convert the original x row vector into a column vector, as far as this program is concerned, the row vector and the column vector will not affect the final plot, so it doesn't matter if you add it or not.

The owner of the second formula checks to see if there is a mistake.

The fourth formula is representation.

The elements in x1 are taken as 0, 1, and 2 ,......12 and then divide by 2, ie.

x1=[0,1/2,1,3/2,…,6]

It should be noted that in MATLAB.

Generally it represents a loop, and its format is generally a:b:c, where a is the initial value, b is the step size, and c is the termination value, similar to the c language, for(i=a; i≤c;i=i+b）

If Jiling B is default, that is, A:C, it means that the default step size is 1.

Take the first x as an example, x=(0:pi 100:2*pi), which represents a row vector.

x=[0,pi/100,2*pi/100,3*pi/100,…, 2*pi], if there is a matrix in the future, there will often be a writing like a[1:20,3:15], which is actually the element of the matrix a from the first row to the 20th, and the third to the 15th column.

Finally, note the similar formula y2=2*exp(; *No* is because X is a vector (matrix) here, if you use * only to do the multiplication of the missing representation vector, it will generally prompt you to what dimension does not match what is wrong pure lead argument, in fact, because y2 here actually wants to carry out element-level operations, that is, each element in x performs some operations to get a y2 value, so "

Representation is an element in x to operate.

1. You opened the file with Notepad, right? If you open it with another device (e.g. word, ultraedit), you can see the effect of line breaking.

2. Put fid=fopen('','w');

Changed to fid=fopen('','wt');

It can achieve the effect of line breaking.

The original way you wrote it was to open the file in binary mode, and the next suggested way is to open it in text mode. On Windows, the main function of opening a file in text mode is to write a newline (), a carriage return (), and if it's a separate line break, Notepad will only appear as a small black square.

3. Another way to change is that the way to open the file remains the same, but putInstead。Obviously, this method is more cumbersome.

4. You said "After removing, the txt file can't be opened", it shouldn't be. However, it is also possible that the lines are too long and there is a problem with the display.

I don't know what your educational level is, I'll try to keep it simple.

Ordinary integral: Generally speaking, the integrand is foundOriginal function, and then put the upper and lower limitsBring in the evaluation(definite integral).

The solution isExact solution

See University course: Advanced Mathematics

Functions available in MATLAB:int（），Solving.

Numerical Integral: Due to inPractical engineeringThe vast majority of points areUnable to find the original function

Therefore, it is very difficult to get an exact solution.

In order to be able to calculate the results, some big bulls (Newton, Gauss, etc.) came up with itNumerical solution

Namely:Numerical integration(The error with the exact solution satisfies the need).

There are many ways to do this, such as:

trapezoidal formula; Simpson Formula; recursive formulas; Dragonberg Integral; adaptive integration; Gauss-Legendre points and much more.

See Graduate Program: Numerical Analysis

In MATLAB, there are some functions for finding numerical integrations:

trapz(): Based on the compound trapezoidal formula.

integral(): solves the unary numerical integral.

integral2(): solves the numerical solution of the double integral of the general region.

integral3(): solves the numerical solution of the triple integral of the general region.

Personally, I use the Gaussian quadratic method most often to find numerical integrals.

Generally speaking, 10-20 Gaussian points can be used to obtain a numerical solution with sufficient accuracy.

Finally: Please call me Lei Feng!