# Homework Help: 3D Plotting - Tornado Figure

1. Jun 21, 2011

### GreenPrint

1. The problem statement, all variables and given/known data

Hi,

I'm taking Intro to Computing for Engr. and my highest level math course I have taken is Calculus I. I'm trying to solve this problem in my book for Intro to Computing for Engr. and believe that the math is over my head. This may well be the case. But sense this is a course in which I'm trying to learn how to use MATLAB and not whatever math course in which I would learn how to do such a thing as in the title so I'm kind of lost as to what to do. It's not that I need help using MATLAB I just need help with the math.

5.28

See the first attachment, it's Figure P5.28 in the book

"Figure out how to adjust your input to plot3 in Problem 5.27 so as to create a graph that looks like a tornado. (See Figure P5.28.) Use comet3 instead of plot3 to create the graph."

Note that the plot3 command just plots in three dimensions and comet3 is a command that just plots in three dimensions but allows the use to view the graph being plotted. The inputs to both commands are just the x values, the y values, and the z values.

Alright problem 5.27 had me plotting a three dimensional graph were
x=[0:pi/100:20*pi]
Note that this is just all the values that occur from 0 to 20*pi by increments of pi/100
y = x sin(x)
z = x cos(x)

The resulting graph that I got when I graphed it using the plot3 command is the second attachment.

Alright I have no idea how to manipulate plot3(x,y,z), (see were I defined x, y, and z), to get the tornado figure and was hoping someone could point me in the right direction in some way shape or form.

Thanks!

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

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• ###### snip2.JPG
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2. Jun 22, 2011

### HallsofIvy

The problem does not say "manipulate plot3(x, y, z)". It says alter your input. What is your input for 5.27?

3. Jun 22, 2011

### GreenPrint

it's just
plot3(x,y,z)
were
x=[0:pi/100:20*pi]
y = x sin(x)
z = x cos(x)

4. Jun 22, 2011

### GreenPrint

Here's the original problems. The problems are exactly the same but the numbering is different because it's from the first version of the book but were using the second version in our course. I got the first version on my computer. The wording is exactly the same as that of my book the numbering is just different.

Here's what I did for 5.27, and the resulting graph for part (c) is the second attachment for the first post, and is what is being referred to in the next problem which I'm completely lost as to were even to begin

%5.27
x=[0:pi/100;20*pi];
y=[x.*sin(x)];
z=[x.*cos(x)];
%(a)
plot(x,y)
title('xsin(x)');
xlabel('x');
ylabel('xsin(x)');
grid on
%(b)
polar(x,y)
title('xsin(x)');
grid on
%(C)
x=[0:pi/100;20*pi];
y=[x.*sin(x)];
z=[x.*cos(x)];
plot3(x,y,z)
title('xsin(x) & xcos(x)');
xlabel('x');
ylabel('xsin(x)');
zlabel('xcos(x)');
grid on

#### Attached Files:

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• ###### 5.28222.JPG
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5. Jun 22, 2011

i got it