How do I append text after an answer in Octave? - octave

I am new to Octave and I've written the following function to combine sound pressure levels. I want to present the answer with a reference value after it. e.g.: 83 dB re: 20µPa rather than just 83, but I don't know how to add the text after the answer.
function L_total = combineLevels(Lp)
x = Lp./10;
y = 10.^x; z = sum(y);
L_total = 10*log10(z);
endfunction
Any advice would be appreciated. Thanks!

Sounds like you want to use fprintf or sprintf. These functions allow you to construct strings that interpolate values from variables. Try:
fprintf('%d dB re: %duPa\n', L_total, Lp);

Related

Plot on higher time frame. Security, mutable variable, global variable, function problem

I'm trying to plot the same shape from the 15 min onto the Daily as well. This is the code to plot a shape on the 15 min which works fine;
if crossover(s3K,s3D) and s3K<25 and (s4K-s4D<3 and s4K-s4D>-3) and s4K<35//or s4D-s4K>0 and s4D-s4K<1 and s4K<50 and s1K<40
rwCross:=true
plotshape(rwCross, style = shape.arrowup, location = location.belowbar, color=color.yellow, size=size.small)
But to plot it on the daily i've tried;
rwCrossDaily = security(syminfo.tickerid,'D', rwCross)
plotshape(rwCrossDaily, style = shape.arrowup, location = location.belowbar, color=color.yellow, size=size.small)
Which gives me the mutable variable error. So i tried using a function to get around it;
rwCross_func() =>
if crossover(s3K,s3D) and s3K<25 and (s4K-s4D<3 and s4K-s4D>-3) and s4K<35//or s4D-s4K>0 and s4D-s4K<1 and s4K<50 and s1K<40
rwCross:=true
rwCrossDaily = security(syminfo.tickerid,'D', rwCross_func())
But now it tells me I 'Cannot modify global variable 'rwCross' in function.'
Help please!
Best solution and cleanest solution here is to just make a bool out of your condition in its simplest form:
rwCross = crossover(s3K,s3D) and s3K<25 and (s4K-s4D<3 and s4K-s4D>-3) and s4K<35//or s4D-s4K>0 and s4D-s4K<1 and s4K<50 and s1K<40
rwCross will naturally become true without the if. This way we do not need to have anything mutable, although there are more solutions for situations that we must...
Cheers!

Storing matlab array in MySQL. Again

I have a 3D array in Matlab of uint16(basically it is just an image 1080x1920x3). I want to store it in mysql. Here is what I'm doing:
MySQL:
create table imgtest(img longblob);
Matlab:
% image_data - is my image as described before
raw_im = reshape(image_data,1,[]);
conn = database('test','root','root','Vendor','MySQL','Server','localhost')
x = conn.Handle;
insertcommand = ['INSERT INTO imtest (img) values (?)'];
StatementObject = x.prepareStatement(insertcommand);
StatementObject.setObject(1,raw_im)
StatementObject.execute
The problem is that I'm writing about 600k uint16 values into this blob field. But when I take this field from the DB, I always getting about 1.2 million of uint8 elements(exactly two times more).
So, is there a way to read this byte field as a set of uint16, but not uint8?
Thank you.
I have been doing something similar for one of my projects
basically there was one difference but maybe it would clarify something to you.
I was loading image directly to DB from file with command:
INSERT INTO BaseImage(Image)
SELECT * FROM OPENROWSET(BULK N'C:\co.jpg', SINGLE_BLOB) as image
and getting it back to Matlab required typecasting (just like #sebastian mentioned)
SQL_query = 'select TOP 1 pk_BaseImage,Image from BaseImage order by pk_BaseImage desc';
[data] = SQL_query_exec(SQL_query);
pk_BaseImage = data.Data.pk_BaseImage;
out = typecast(data.Data.Image{1,1},'uint8');
BUT..
it was not enough, I had to do some trick to use 'out' as image
I was forced to write it to temporary file and read it again to Matlab (I know it's strange but it worked very well and I could for example calculate DWT, DFT and so on)
image_matrix = get_image_matrix( out );
get_image_matrix function looks like:
function [ out ] = get_image_matrix( input )
targetfilename = 'temp.jpg';
%wynik
fid = fopen(targetfilename,'w');
if fid
fwrite(fid,input,'uint8');
end
fclose(fid);
out = imread(targetfilename);
delete(targetfilename);
end
I hope it will help you :)
One important notice - I used gray-scale images (uint8 type)
You can most probably typecast the uint8's into uint16's to get back at your original image data:
uint16_result = typecast(uint8_result, 'uint16');
I'm not familiar with the database toolbox - so there might well be a way to tell Matlab to do this on its own.
OK, thank you both. I've summarized your answers and this what I've got:
Since blob field is nothing more than byte array, then we should cast our data in matlab before writing it to the DB. After reading it from DB, we should cast them back.
Minimum working example is:
MySQL
create table imgtest(img longblob);
Matlab
% image_data - is my image as described before
raw_im = typecast(reshape(image_data,1,[]),'uint8'); %! the main string
conn = database('test','root','root','Vendor','MySQL','Server','localhost')
x = conn.Handle;
insertcommand = ['INSERT INTO imtest (img) values (?)'];
StatementObject = x.prepareStatement(insertcommand);
StatementObject.setObject(1,raw_im)
StatementObject.execute
After we can read it back:
res = exec(conn,'Select * from imtest')
array_uint8 = fetch(res);
array_uint8 = array_uint8{1};
array_uint16 = typecast(array_uint8,'uint16').
Hope this will help someone.

Calling function with changing input parameters in a loop Matlab

I have caught myself in a issue, I know its not that difficult but I couldnt figure out how to implement it. I have an m file that looks like
clear;
PVinv.m_SwF=20e3
for m=1:1:70;
PVinv.m_SwF=PVinv.m_SwF+1e3;
Lmin = PVinv.InductanceDimens();
Wa_Ac = PVinv.CoreSizeModel();
PVinv.CoreSelect(Wa_Ac);
[loss_ind_core,loss_ind_copper] = PVinv.InductorLossModel(PVinv.m_L_Selected);
Total_Inductor_Loss=loss_ind_core+loss_ind_copper
plot(PVinv.m_SwF,Total_Inductor_Loss,'--gs');
hold on
xlim([10e3 90e3])
set(gca,'XTickLabel',{'10';'20';'30';'40';'50';'60';'70';'80';'90'})
grid on
xlabel('Switching Frequency [kHz]');
ylabel('Power loss [W]');
end
And the function that is of interest is CoreSelect(Wa_Ac)
function obj = CoreSelect(obj, WaAc)
obj.m_Core_Available= obj.m_Core_List(i);
obj.m_L_Selected.m_Core = obj.m_Core_Available;
end
I want to change the value of i from obj.m_Core_List(1) to obj.m_Core_List(27) within that for loop of main m file. How can I get the value of the function coreselect when I call it in main m file
For eg for m=1 to 70 I want the function to take the value of i=1 then execute till plot command and then same with but i=2 and so on
Any suggestion would be really helpful
I'm not sure I understand your question perfectly, but I think you want to pass an index i to the CoreSelect function, and loop i from 1 to 27 outside of the function. Try this:
function obj = CoreSelect(obj, WaAc, i)
...
end
for i=1:27,
PVInv.CoreSelect(WaAc,i);
end

Lua - How do I use a function from another script?

I've been looking around and I have not been able to find anything that has worked for me. I'm starting to learn more Lua and to start off I'm making a simple calculator. I was able to get each individual operation onto separate programs, but when I try to combine them I just can't get it to work. My script as it is now is
require "io"
require "operations.lua"
do
print ("Please enter the first number in your problem.")
x = io.read()
print ("Please enter the second number in your problem.")
y = io.read()
print ("Please choose the operation you wish to perform.")
print ("Use 1 for addition, 2 for subtraction, 3 for multiplication, and 4 for division.")
op = io.read()
op = 1 then
function addition
op = 2 then
function subtraction
op = 3 then
function multiplication
op = 4 then
function division
print (answer)
io.read()
end
and my operations.lua script is
function addition
return answer = x+y
end
function subtraction
return answer = x-y
end
function multiplication
return answer = x*y
end
function division
return answer = x/y
end
I've tried using
if op = 1 then
answer = x+y
print(answer)
if op = 2 then
answer = x-y
print(answer)
and I did that completing each operation. But it doesn't work. I can't even get the error code that it's returning because it closes so fast. What should I do?
In your example, make these changes: You require operations.lua without the extension. Include parameters in your operations function definitions. Return the operation expression directly versus returning a statement like answer = x+y.
All together:
Code for operations.lua
function addition(x,y)
return x + y
end
--more functions go here...
function division(x,y)
return x / y
end
Code for your hosting Lua script:
require "operations"
result = addition(5,7)
print(result)
result = division(9,3)
print(result)
Once you get that working, try re-adding your io logic.
Keep in mind that as it's coded, your functions will be defined globally. To avoid polluting the global table, consider defining operations.lua as a module. Take a look at the lua-users.org Modules Tutorial.
The right if-then-else syntax:
if op==1 then
answer = a+b
elseif op==2 then
answer = a*b
end
print(answer)
After: please check the correct function-declaration syntax.
After: return answer=x+y is incorrect. If you want set answer's value, set without return. If you want return the sum, please use return x+y.
And I think you should check Programming in Lua.
First of all, learn to use the command line so you can see the errors (on Windows that would be cmd.exe).
Second, change the second line to require("operations"). The way you did it the interpreter expects a directory operations with an underlying script lua.lua.

Octave and multiple Bode plots

I'm teaching myself Octave and as a motivational exercise am attempting to create some Bode plots. I'd like to create a plot that has multiple curves for different values of a parameter in a transfer function, for example the time constant of a simple RC filter. I'm trying to do it as follows:
tau = [1,2,3]
for i = tau
g(i) = tf(1,[tau(i),1])
endfor
bode(g(1),g(2),g(3))
But it doesn't work, I get the error
error: octave_base_value::imag (): wrong type argument `struct'
However, it works fine if there are not multiple arguments to the bode command and the last line is simply:
bode(g(1))
Any advice as to where I've gone wrong would be appreciated - is there a better way to do what I want to do?
I was able to do it with the following sequence (with octave 3.2.4 on debian):
bode(g(1))
set (findobj (gcf, "type", "axes"), "nextplot", "add")
bode(g(2))
bode(g(3))
The second command is similar to hold on but it works when there are subplots; I found it here.
Using your own code:
subplot(211), hold on
subplot(212), hold on
tau = [1,2,3]
for i = 1:length(tau),
g(i) = tf(1,[tau(i),1]);
bode(g(i))
endfor
The problem with this solution is that you cannot identify a specific plot. You cannot access figure properties through bode() function directly.
Here then a plausible solution to bring you colorful plots:
colorsplot = ["b","m","g"]
tau = [1,2,3]
g = tf(1,[tau(1),1]);
[mag, ph, w] = bode(g);
subplot(211), semilogx(w,20*log(mag)), hold on
subplot(212), semilogx(w,ph), hold on
for i = 2:length(tau),
g = tf(1,[tau(i),1]);
[mag, ph, waux] = bode(g,w);
subplot(211), semilogx(w,20*log(mag),colorsplot(i))
subplot(212), semilogx(w,ph,colorsplot(i))
endfor