格式化绘图：
1.color：
| b | g |
r | c | m | y | k | w |
| blue | green | red | cyan | magenta | yellow | black | white |
2.type of coordinate point
| . | o | x | + | * | s | d | v | ^ | < | > | p | h |
| point | circle | x-mark | plus | star | square | diamond | triangle (down) | triangle (up) | triangle (left) | riangle (right) | pentagram（五角星形） | hexagram（六角星形） |
3.type of line
| - | : | -. | -- | (none) |
| solid | dotted | dashdot | dashed(虚线) | no line |
4.instance
by using the instruction "polt(X, Y, S)", we can plot points and lines with the types listed above. in "polt(X, Y, S)",X and Y are vectors, S is a string formed of elements listed above. For example, when S = 'o--', it means that the symble for points is circle, and the line format is dashed.
conduct the instructions：
>> x = [1:1:10];
>> y = [2:1:11];
>> plot(x, y, 'o--')
we can get figure below:
