Question

matlab help please

Answer 1

% 6.10 This problem requires you to generate temperature-conversion tables.
% Use the following equatioins, which describe the relationships between
% temperature in degrees Fahrenheit (Tf), degrees celcius (Tc), kelvin
% (Tk), and degrees Rankine (Tr), respectively.
% Tf = Tr - 459.67 degrees R
% Tf = 9/5*Tc + 32 degrees F
% Tr = 9/5*Tk

% (a) Create a function called F_to_K that converts temperatures in
% Fahrenheit to Kelvin. Use your function to generate a conversion table
% for values from 0* to 200* F.

Tf = 0:200; % Fehrenheit vector from zero to two-hundred
c6p10a = FK(Tf); % called c6p10a = Tk, this formula is to use to find kelvins

% table displays ouptut of F and K
F_K = [Tf; c6p10a]'

% (c) Create a function called C_to_F that converts temperature in Celsius
% to Fahrenheit. Use your function to generate a conversion table from 0T*
% to 100* C. Choose an appropriate spacing.

Answer 2

function F_to_K = FK(k)

% this function converts degrees Fahrenheit to Kelvin
F_to_K = (5/9)*(k+459.67);

Answer 3

The reason I named FK(Tf) c6p10a is because my instructor wants us to use his variable formatting.

Answer 4

@jim_thompson5910

Answer 5

part a @jim_thompson5910

Answer 6

ok let me look it over

Answer 7

okay

Answer 8

does your teacher want you to create a separate m file for the function? or have you put the function inside this current m file?

Answer 9

Formatting and the hw assignment

Answer 10

I don't think he does base on the schedule, 2nd one

Answer 11

`Unless there is a reason not to, begin each problem with the clear and clc commands`

so don't forget about that

Answer 12

hmm it makes no mention of functions

Answer 13

okay, I won't. So how does my function look? I can't get it to run, says there is a problem with line c6p10a = Fk(Tf)

Answer 14

Put look at hw 6 on schedule.

Answer 15

Even look at the description of the problem 6.10, posted

Answer 16

you mean this?

`Turn in 3 function m-files: F_to_K.m, C_to_F.m,`
`& temperature_conversions.m only. No hw5.m`
`required. Use HW format reqmnts`

Answer 17

Yes, so I won't turn in 6.10 coding. But I made them for my use.

Answer 18

ok, so you'll need to make the m file `F_to_K.m` and name the function `F_to_K`

the function name and the m file name must match up so matlab can find the right function from the right file. If there isn't a match, matlab will let you know with an error

Answer 19

`c6p10a = FK(Tf); % called c6p10a = Tk, this formula is to use to find kelvins`

this line is invalid because FK is the wrong function name.

Answer 20

okay let me think about this for a bit.

Answer 21

Yes, got it.
Tf = 0:200; % Fehrenheit vector from zero to two-hundred
c6p10a = F_to_K(Tf); % called c6p10a = Tk, this formula is to use to find kelvins

% table displays ouptut of F and K
F_K = [Tf; c6p10a ]'

Answer 22

looks good

Answer 23

okay so F_to_k(Tf) has to match the F_to_K m file? What part needs to match?

Answer 24

F_to_k is the name of the function

it MUST match the name of the m file exactly. One character off and matlab won't be able to find the proper file

Answer 25

so if your teacher wants you to call the m file `F_to_k.m` then you must name the function `F_to_k`

Answer 26

Yes, I agree with the statement above. What about under 6.10? I called it homework5 so it's homework5.m

Answer 27

on the line `c6p10a = FK(Tf);` you're calling some function `FK` which matlab will look through the directories (it is told to look through) for the m file `FK.m` but it may not find it. If it does find it, you may be looking in the wrong m file

Answer 28

okay I see what you are saying now. Than answers my question.

Answer 29

did you make a function called homework5?

Answer 30

No, I didn't make a function called homework 5. My understanding is that I need the m file homework5 because that is where I put my vector and the table formula. ALso I need homework5 m file so I can ouput the conversions.

Answer 31

I see

Answer 32

I may email my instructor to double check with him as to whether or not he wants a homework5 m file. There is a possibility he wants just the function m files because he has the other information from each problem.

Answer 33

Basically I had to make homework5 m file to see if my functions work.

Answer 34

I think your prof is looking for only the function files. Since it says `No hw5.m required`

but you'll still need your hw5.m file to test out the functions to see if they work or not

Answer 35

Okay I see. Sounds good. Thanks for your help. If I have any additional questions I will tag you.

Answer 36

@jim_thompson5910 subfunctions? I have to re do problem 6.10 but use subfunctionns

%% 6.15 In Problem 6.10 you were asked to create and use three different
% temperature conversion functions, based on the following conversion
% equations:
% Tf = Tr - 459.67 degrees R
% Tf = 9/5*Tc + 32 degrees F
% Tr = 9/5*Tk
% Recreate Problem 6.10 using nested subfunctions. The primary function
% should be called temperature_conversions and should include the
% subfunctions
% F_to_k
% C_to_R
% C_to_F
% Within the primary function use the subfunctions to:

clc; clear % clears command and workspace window

% (a) Generate a conversion table for values from 0*F to 200*F. Include a
% column for temperature in Fahrenheit and Kelvin.

Answer 37

So these subfunctions would be in the current m files I have for the two separate functions or do I need to make one m file with many function in it?

Answer 38

here's an example of what your teacher wants

http://www.mathworks.com/help/matlab/matlab_prog/local-functions.html

Answer 39

Okay I will take a look at it and let me think about this.

Answer 40

see attached. I took a screenshot of that page and I go over the example of where the function and subfunctions are (where they start and end)

Answer 41

@jim_thompson5910

Answer 42

let me think

Answer 43

having a bit of a hard time figuring out the conv_table ? My understanding is that each function should output the conversion factor given Tf?

Answer 44

no, what I think is supposed to happen is that you

step 1) go from Fahrenheit to Celsius

step 2) go from Celsius to Kelvin

then you make a table with the x column being the Fahrenheit and y column being the Kelvin

Answer 45

the subfunctions won't show what is going on. Only the final result is shown. This is to avoid clutter

Answer 46

so what you are saying is only make two sub functions? It asks to make three sub functions?

Answer 47

But I see what you are saying. Basically have the program do the math portion.

Answer 48

Let me think about this some more and figure it out.

Answer 49

hmm I guess Rankine has to be in there too. Tbh, this is the first time I've ever seen Rankine before

Answer 50

Well I solved for Rankine on paper. So I am going to have 3 temp_conv m files for this part of the assignment?

Answer 51

I think so

Answer 52

I found the Rankine formula from the other two formulas

Answer 53

Let me think about this

Answer 54

where is your part b?

Answer 55

part C, he asked us only to do part a and c

% (c) Recall that you will need to call your primary function from the
% command window or from a script M-file.

Answer 56

ah ok

Answer 57

I will figure this part out later

Answer 58

Can I offer a suggestion? I noticed you wrote F_to_K as one of your variable names. That's a bit clunky. The ouptut of the FK function is the kelvin temperature, so why not just call the output K? Instead of F_to_K

Answer 59

and there's a problem with your temperature_conversions function

x is the input

x is what exactly? The temperature in Celsius? The temperature in Fahrenheit?

Answer 60

because I am a complicated person lol

No, thanks for the suggestion. I will change it to K.

Sometimes I am writing this code I just use what is available. Sometimes I have a hard time naming variables because I am trying to organize the info in my head so I just start using what ever variables sounds reasonable.

Answer 61

Yes, I don't know what the x represents in the temperature_conversion(x) I am still trying to understand what x represents relating to the other variables like k, f, c

Answer 62

F_to_K is better suited as a function (or subfunction) name

Answer 63

Take for example this code

function [avg, med] = mystats(x)
n = length(x);
avg = mymean(x,n);
med = mymedian(x,n);
end

function a = mymean(v,n)
% MYMEAN Example of a local function.

a = sum(v)/n;
end

function m = mymedian(v,n)
% MYMEDIAN Another example of a local function.

w = sort(v);
if rem(n,2) == 1
m = w((n + 1)/2);
else
m = (w(n/2) + w(n/2 + 1))/2;
end
end

Answer 64

x is the input of the `temperature_conversions` function

x gets fed into the FK, CR, CF subfunctions

so there's a mismatch in units when you have Fahrenheit for the first subfunction but Celsius for the other subfunctions

Answer 65

what's your question about that example?

Answer 66

looking at a = mymean(v,n) this has v and n but no x

Answer 67

it only has v and n in the formula a = sum(v)/n;

Answer 68

so you're wondering why no x?

Answer 69

How does that relate to function [avg, med] = mystats(x)

Answer 70

yes

Answer 71

well x is used but probably not in the way you think

n is dependent on x

n = length(x);

gets the size of x (ie how many numbers we're dealing with)

Answer 72

avg = mymean(x,n);

calls the `mymean` function

first input is x
second input is n

go to the definition of `mymean` and we see this line

function a = mymean(v,n)

so the first input is v, the second input is n

match up the inputs

v = x
n = n

Answer 73

so they could have said

function a = mymean(x,n)

but chose to go with v instead

Answer 74

okay

Answer 75

Okay so I need 3 temperature_conversions m files each function will have 1 to 2 subfunctions depending on how many equations are involved?

Answer 76

I think you'll have 3 subfunctions based on what you wrote

% Tf = Tr - 459.67 degrees R
% Tf = 9/5*Tc + 32 degrees F
% Tr = 9/5*Tk

Answer 77

^So those are the sub functions? So then these equations are not sub functions

% first subfunction FK
function a = FK(f)

a = (5 / 9) * (f + 459.67);
end

% second subfunction CR
function b = CR(c1)

b = (9 / 5) * (c1 + 273.15);
end

% third subfunction CF
function c = CF(c2)

c = (9 / 5) * (c2 + 32);
end

Answer 78

These are the equations that make the conversion

Answer 79

hmm I'm still having an issue with how you set up the inputs

Answer 80

let me think of how to fix that

Answer 81

kk

Answer 82

I think I may have something. One moment.

Answer 83

ok I had to make two separate m files. I'm not sure how else to work it

Answer 84

why not 3?

Answer 85

here is the first one where the inputs are all in celsius

Answer 86

take note how each subfunction has the same input: temp in Celsius

Answer 87

well except the K_to_R one

for some reason I forgot to delete it

Answer 88

brb I need to take care of something

Answer 89

ok

Answer 90

@jim_thompson5910

Answer 91

Tf = 0:200; % Fehrenheit vector from zero to two-hundred
c6p15a = temperature_conversions(Tf); % c6p15a = temp_conv which finds


% these are the set of subfunctions that will be used to solve for kelvin
% given fahrenheit
% this function temperature_conversions has the input
% of fahrenheit which will given rankine, then input rankine to get kelvin
function [R, K] = temperature_conversions(Tf)

R = F_to_R(Tf);
K = R_to_K(Tf);
end

% function to solves for rankine given fahrenheit
function R = F_to_R(F)

R = F + 459.67;
end

% function solves for kelvin given rankine
function K = R_to_K(R)

K = (5/9)*R;
end