lecture_05.md

%plot --format svg

Questions from last class

When you execute the given function

my_function.m:

function [x,y] = my_function(max_time)
    N=100;
    t=linspace(0,max_time,N);
    x=t.^2;
    y=2*t;
end

as

>> [x,y] = my_function(20);

What variables are saved to your workspace?

How do you write a help description for a function?

How to keep our forked ME3255S page up to date with the original pretty tired this morning

How do I use the Github Desktop?

whats your favorite football team?

Will UConn's github get updated to the newest version of github? As u said in class trail and error is the best way of learning.

I believe the % is the same as matlab where it de-links your code into text

Does the @ symbol designate a pointer?

Given the change of air pressure as altitude increases, how fast would a frisbee have to travel (and spin) to hit an airplane?

What is a gui?

could you go over a nested for loop example

Can't seem to get this function to produce any graph and am not sure why

When are these google forms due?

how do I create a new function using Github on my desktop?

Can you explain the first question more in class?

What is the meaning of life?

Should I just know how or what these topics are or will we learn them in the future?

f =@(x) x.^2

f = 

    @(x)x.^2

f([1:2:10])
f(4)

ans =

     1     9    25    49    81


ans =

    16

% nested for loop example
for i = [1:6]
    for j = [1:3]
        fprintf('i=%i and j=%i\n',i,j)
    end
end
        

i=1 and j=1
i=1 and j=2
i=1 and j=3
i=2 and j=1
i=2 and j=2
i=2 and j=3
i=3 and j=1
i=3 and j=2
i=3 and j=3
i=4 and j=1
i=4 and j=2
i=4 and j=3
i=5 and j=1
i=5 and j=2
i=5 and j=3
i=6 and j=1
i=6 and j=2
i=6 and j=3

From last class

help my_function

Help documentation of "my_function"
  This function computes the velocity in the x- and y-directions given
  three vectors of position in x- and y-directions as a function of time
  x = x-position
  y = y-position
  t = time
  output
  vx = velocity in x-direction
  vy = velocity in y-direction

help my_caller

Help documentation of "my_caller"
  This function computes the acceleration in the x- and y-directions given
  three vectors of position in x- and y-directions as a function of time
  x = x-position
  y = y-position
  t = time
  output
  ax = acceleration in x-direction
  ay = acceleration in y-direction

t=linspace(0,10,100)'; 
x=t.^3; % vx = 3*t^2
y=t.^2/2;  % vy = t
[vx,vy]=my_function(x,y,t);
[ax,ay]=my_caller(x,y,t);
yyaxis left
plot(t(1:10:end),ax(1:10:end),'o',t,6*t)
ylabel('a_{x}')
yyaxis right
plot(t(1:10:end),ay(1:10:end),'s',t, 1*t./t)
ylabel('a_{y}')
xlabel('time')
axis([0,10,0,3])

diff_match_dims(x,t)

�[0;31mUndefined function 'diff_match_dims' for input arguments of type 'double'.
�[0m

Good coding habits

naming folders and files

Stanford file naming best practices

1. Include information to distinguish file name e.g. project name, objective of function, name/initials, type of data, conditions, version of file,
2. if using dates, use YYYYMMDD, so the computer organizes by year, then month, then day
3. avoid special characters e.g. !, #, $, ...
4. avoid using spaces if not necessary, some programs consider a space as a break in code use dashes - or underscores _ or CamelCase

Commenting your code

Its important to comment your code to mention what a variable's units are, what the function is supposed to do, etc.

function i=code(j)
    % Example of bad variable names and bad function name
    for w=1:j
        i(w)=w;
    end
end

�[0;31mError: Function definitions are not permitted in this context.
�[0m

help code

code not found.

Use the Help browser search field to search the documentation, or
type "help help" for help command options, such as help for methods.

Choose variable names that describe the variable

function count_vector=counting_function(max_value)
    % Good variable names and better help documentation
    % 
    % counting function creates a vector from 1 to max_value where each index, i, is 
    % stored in each vector spot
    for i=1:max_value
        count_vector(i)=i; % set each element in count_vector to i
    end
end      

help counting_function

'counting_function' is a command-line function

 Good variable names and better help documentation
 
 counting function creates a vector from 1 to max_value where each index, i, is 
 stored in each vector spot


Additional help for built-in functions and operators is
available in the online version of the manual.  Use the command
'doc <topic>' to search the manual index.

Help and information about Octave is also available on the WWW
at http://www.octave.org and via the help@octave.org
mailing list.

Putting it all together

1. Clone your homework_1 to your computer
2. open Matlab (cli, jupyter or gui)
3. Change working directory to homework_1 e.g. Windows:cd('C:\Users\rcc02007\Documents\Github\homework_1'), Mac: cd('/Users/rcc02007/Documents/Github/homework_1')
4. You have already created your first script setdefaults.m (if not see lecture_4)
5. Run >> setdefaults.m
6. Create a new m-file called nitrogen_pressure.m
7. Create a function based upon the ideal gas law for nitrogen, Pv=RT
   1. R=0.2968 kJ/(kg-K)
   2. inputs to function are v (specific volume m^3/kg), and T, temperature (K)
   3. output is P, pressure (kPa)
8. Once the function works, commit the change to the repository (add a message, like 'added file nitrogen_pressure.m'
9. After file is 'committed', 'push' the changes to your github account

for the command-line git user, this is steps 8 and 9:

1. $ git add *
2. $ git commit -m 'added file nitrogen_pressure.m'
3. $ git push -u origin master Username for 'https://github.uconn.edu':rcc02007 <enter> Password for 'https://rcc02007@github.uconn.edu':

Now, use this function to plot the range of pressures that a pressure vessel would experience if it is 1000 gallons (3.79 m^3) with 10-20 kg of Nitrogen and temperatures range from -10 to 35 degrees C.

v=0.379/linspace(50,20,10);
T=273.15+linspace(-10,35,10);
[v_grid,T_grid]=meshgrid(v,T);
P = nitrogen_pressure(v,T);
pcolor(v_grid,T_grid,P)

setdefaults;
v=3.79./linspace(10,20,10);
T=273.15+linspace(-10,35,10);
[v_grid,T_grid]=meshgrid(v,T);
P = nitrogen_pressure(v_grid,T_grid);
pcolor(v_grid,T_grid-273.15,P-100)
xlabel('specific volume (m^3/kg)')
ylabel('Temperature (C)')
%zlabel('Pressure (kPa)')

%colormap winter
%colormap summer
%colormap jet
colorbar()