如何在MATLAB中对图形的因变量执行语句? [英] How do I perform statements on the dependent variable of a graph in MATLAB?

问题描述

我想知道如何从间隔中获取特定数字以对其进行测试，然后能够在一个图形下构建不同的函数.例如(在本例中为'x'变量)

I would like to know how to grab a specific number from an interval to test it and later be able to built a different functions under one graph. For example (in this case the 'x' variable),

 x 0:.5:5;

 Ids=ones(x);
 figure;hold on;

 for n = 1:5
     if(x < 3.0) %problem here
         Ids(n) = plot(x,x.^x);
     else 
         if (x > 4.0)  %and here
            Ids(n) = plot(x,-x.^x);
         end
     end
 end

编辑

我真正想在MATLAB中做的是能够执行以下分段功能:

What I really want to do in MATLAB is to be able to do the following piecewise function:

y(x) = {  0                   (t - 5) < 0
       { (t - 5)*(t - x)      x < (t - 5)
       { (t + x^2)            x >= (t - 5)

由于x = 0:.5:10和t = 0:.1:10，我似乎不了解如何绘制此函数的图形.我知道如何在没有t的情况下执行此操作，但是当包含t并且与x的间隔不同时，我迷路了.

I don't seem to understand how to graph this function since x = 0:.5:10 and t = 0:.1:10. I know how to do this without the t, but I get lost when the t is included and has different intervals compared to the x.

推荐答案

从您的代码中尚不清楚您要做什么，但是似乎您要创建并绘制具有以下内容的函数f(x)形式:

It's a little unclear from your code what you are trying to do, but it appears that you want to create and plot a function f(x) that has the following form:

f(x) = [ x     for 3 <= x <= 4
       [ x^x   for x < 3
       [ -x^x  for x > 4

如果这是您要执行的操作，则可以使用逻辑索引:

If this is what you want to do, you can do the following using logical indexing:

x = 0:0.5:5;  %# 11 points spaced from 0 to 5 in steps of 0.5
y = x;        %# Initialize y
index = x < 3;                   %# Get a logical index of points less than 3
y(index) = x(index).^x(index);   %# Change the indexed points
index = x > 4;                   %# Get a logical index of points greater then 4
y(index) = -x(index).^x(index);  %# Change the indexed points
plot(x,y);                       %# Plot y versus x

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