下面是一段matlab程序，画曲线用的。 但不知道最后一句里的”--rs“是什么意思。请教一下大家了！

传递给plot的一个曲线绘制参数.
matlab help里有解释.我使用时一般都默认.
色彩字符颜色线型字符线型格式标记符号数据点形式标记符号数据点形式
y 黄- 实线. 点< 小于号
m 紫： 点线o 圆s 正方形
c 青-. 点划线x 叉号d 菱形
r 红- - 虚线+ 加号h 六角星
g 绿* 星号p 五角星
b 蓝v 向下三角形
w 白^ 向上三角形
k 黑> 大于号
>>help plot:
PLOT Linear plot.
PLOT(X,Y) plots vector Y versus vector X. If X or Y is a matrix,
then the vector is plotted versus the rows or columns of the matrix,
whichever line up. If X is a scalar and Y is a vector, disconnected
line objects are created and plotted as discrete points vertically at
X.

PLOT(Y) plots the columns of Y versus their index.
If Y is complex, PLOT(Y) is equivalent to PLOT(real(Y),imag(Y)).
In all other uses of PLOT, the imaginary part is ignored.

Various line types, plot symbols and colors may be obtained with
PLOT(X,Y,S) where S is a character string made from one element
from any or all the following 3 columns:

b blue . point - solid
g green o circle : dotted
r red x x-mark -. dashdot
c cyan + plus -- dashed
m magenta * star (none) no line
y yellow s square
k black d diamond
w white v triangle (down)
^ triangle (up)
< triangle (left)
> triangle (right)
p pentagram
h hexagram

For example, PLOT(X,Y,'c+:') plots a cyan dotted line with a plus
at each data point; PLOT(X,Y,'bd') plots blue diamond at each data
point but does not draw any line.

PLOT(X1,Y1,S1,X2,Y2,S2,X3,Y3,S3,...) combines the plots defined by
the (X,Y,S) triples, where the X's and Y's are vectors or matrices
and the S's are strings.

For example, PLOT(X,Y,'y-',X,Y,'go') plots the data twice, with a
solid yellow line interpolating green circles at the data points.

The PLOT command, if no color is specified, makes automatic use of
the colors specified by the axes ColorOrder property. By default,
PLOT cycles through the colors in the ColorOrder property. For
monochrome systems, PLOT cycles over the axes LineStyleOrder property.

Note that RGB colors in the ColorOrder property may differ from
similarly-named colors in the (X,Y,S) triples. For example, the
second axes ColorOrder property is medium green with RGB [0 .5 0],
while PLOT(X,Y,'g') plots a green line with RGB [0 1 0].

If you do not specify a marker type, PLOT uses no marker.
If you do not specify a line style, PLOT uses a solid line.

PLOT(AX,...) plots into the axes with handle AX.

PLOT returns a column vector of handles to lineseries objects, one
handle per plotted line.

The X,Y pairs, or X,Y,S triples, can be followed by
parameter/value pairs to specify additional properties
of the lines. For example, PLOT(X,Y,'LineWidth',2,'Color',[.6 0 0])
will create a plot with a dark red line width of 2 points.

Example
x = -pi:pi/10:pi;
y = tan(sin(x)) - sin(tan(x));
plot(x,y,'--rs','LineWidth',2,...
'MarkerEdgeColor','k',...
'MarkerFaceColor','g',...
'MarkerSize',10)

虚线“——”表示用虚线连接各个点，r表示用红色曲线，s表示用方块标记每个点，总之是在设置曲线显示的属性

--是线型（双短线），r是颜色（红色），s是点型（正方形）