I'm experincing a very weird and erratical behaviour in Lazarus 0.9.30.2 version FPC 2.4.4. as shown in the code snippet below after calling NormalizeVEctor procedure in objects, e1 and ne1 becomes the same value whereas I was intending to preserve the original value of vector in e1 and ne1 will represent the normalized value of that vector.
var
e1,e2, ne1, ne2, bisector, speed,res :QVector2D;
begin
e1 := QVector2D.Create;
e2 := QVector2D.Create;
ne1 := QVector2D.Create;
ne2 := QVector2D.Create;
.....
.....
ne1 := e1;
ne2 := e2;
ne1.NormalizeVector; ne2.NormalizeVector;// ne1 = e1 are the same values
bisector := SubtractVector(ne2,ne1);
QVector declaration is as shown below
QVector2D = class(TPersistent)
public
Vector :TVector3D;
function length: Single;
function NormalizeVector:QVEctor2D;
end;
Related
I am programming a procedure in Maple. This procedure receive a list of vector fields (from the ``DifferentialGeometry'' package). I want that in the output they appear, together with the performed computations, the name of the vector fields introduced by the user.
During the procedure I refer to them by the name I have given to the parameter, but I don't actually know the "names of the variables". Is there a way to recover them? I have being looking for in the Maple documentation and in the DGinfo help, but I didn't get anything.
EXAMPLE ADDED
I have simplified the problem to the following. Consider the code:
with(DifferentialGeometry);
DGsetup([x, u], M);
X := evalDG(D_u*x+2*D_x);
myproc := proc (var)
return evalDG(var+D_u)
end proc;
myproc(X)
The output is
But I want modify the code in such a way that the output were something like
X+D_u is 2 D_x + (1+x) D_u
That is, I want to use the name ("X") of the variable in the output, not only the value (2 D_x + x D_u).
Thank you for your time.
Here is one way of handling your example.
restart;
with(DifferentialGeometry):
DGsetup([x, u], M):
myproc := proc(var::uneval) local evar;
evar := eval(var);
return evalDG(var+D_u) = evalDG(evar+D_u);
end proc:
X := evalDG(D_u*x+2*D_x):
myproc(X);
X + D_u = 2 D_u + (1 + x) D_u
Here is a variant on that idea, with two such parameters on the procedure, but also handling then in a more general manner.
restart;
with(DifferentialGeometry):
DGsetup([x, u], M):
myproc := proc(var1::uneval, var2::uneval)
local evars, res;
evars := [var1=eval(var1), var2=eval(var2)];
res := var1 + var2 + D_u;
return res = evalDG(eval(res, evars));
end proc:
X1 := evalDG(D_u*x+2*D_x):
X2 := evalDG(D_u*x+3*D_x):
myproc(X1, X2);
X1 + X2 + D_u = 5 D_x + (1 + 2 x) D_x
I am very new to structured text, so pardon my simple question.
I am using OpenPLC to create this simple program. I have been following the example from the link below to create flowing lights simple program with structured text. In this video, they used 5LEDs and controlled it with case statements.
However, my question is, if my program needs to turn on 100 lights, how should I change the code?
Should I use for loops? How?
https://www.youtube.com/watch?v=PXnaULHpxC8&t=25s
Yes you can use for loops etc. to make the program more "dynamic".
Unfortunately most of the PLC's don't give you dynamic access to their digital outputs. This means that at the end you will have to write code that will translate the value from array (which you will be looping through) into digital outputs.
There are a few ways to do that. First let me show how you can create chasing light for up to 16.
PROGRAM PLC_PRG
VAR
iNumOfLights : INT := 6;
fbCounter : CTU := ;
fbTicker : BLINK := (ENABLE := TRUE, TIMELOW := T#100MS, TIMEHIGH := T#1S);
wOut: WORD;
END_VAR
fbTicker();
fbCounter(CU := fbTicker.OUT, RESET := fbCounter.Q, PV := iNumOfLights);
wOut := SHL(2#0000_0000_0000_0001, fbCounter.CV);
A := wOut.0;
B := wOut.1;
C := wOut.2;
D := wOut.3;
E := wOut.4;
F := wOut.5;
G := wOut.6;
END_PROGRAM
Or if you know output address you can do it directly to outputs.
PROGRAM PLC_PRG
VAR
iNumOfLights : INT := 6;
fbCounter : CTU := ;
fbTicker : BLINK := (ENABLE := TRUE, TIMELOW := T#100MS, TIMEHIGH := T#1S);
wOut AT %QB0.1: WORD;
END_VAR
fbTicker();
fbCounter(CU := fbTicker.OUT, RESET := fbCounter.Q, PV := iNumOfLights);
wOut := SHL(2#0000_0000_0000_0001, fbCounter.CV);
END_PROGRAM
You can also change type of chasing lights by something like.
IF fbCounter.CV = 0 THEN
wOut := 0;
END_IF;
wOut := wOut OR SHL(2#0000_0000_0000_0001, fbCounter.CV);
Now what is behind this. SHl operator will move 1 to the left on set number. For example SHL(2#0000_0000_0000_0001, 3) will result in 2#0000_0000_0000_1000. So we assign it to wOut and then access individual bits by wOut.[n].
I am receiving data into an array from the energy meters which is of REAL datatype.
My array: ARRAY[0..49] OF Real;
I want to convert this data into string data type like i want all the values enclosed in commas "" separately.
Waiting for your kind responce.
(*Declaration part*)
aMyStringArray : ARRAY[0..49] OF STRING;
aMyRealArray : ARRAY[0..49] OF REAL;
i : INT;
sMyLongString : STRING(50*255);
(*Implementation part*)
sMyLongString := '';
FOR i:=0 TO 49 DO
aMyStringArray[i] := REAL_TO_STRING(aMyRealArray[i]);
sMyLongString := CONCAT(sMyLongString,'"');
sMyLongString := CONCAT(sMyLongString,aMyStringArray[i]);
sMyLongString := CONCAT(sMyLongString,'"');
sMyLongString := CONCAT(sMyLongString,',');
END_FOR
i was "finding Pi" with Monte Carlo Method, but the answer was incorrect. The oryginal code was:
RandomTools[MersenneTwister]: with(Statistics):
tries := 10000:
s := 0;
for i to tries do
if GenerateFloat()^2+GenerateFloat()^2 < 1 then s := s+1 end if;
end do:
evalf(4*s/tries)
It gives answer aroud 2.8-2.85
when I change the code to
s := 0;
x := Array([seq(GenerateFloat(), i = 1 .. tries)]);
y := Array([seq(GenerateFloat(), i = 1 .. tries)]);
for i to tries do
if x[i]^2+y[i]^2 < 1 then s := s+1 end if;
end do:
evalf(4*s/tries)
Then the answer is correct. I have no idea why i can't generate number in "for" loop.
I've founded that the mean of it is the same, but the variance is different.
For:
tries := 100000;
A := Array([seq(GenerateFloat(), i = 1 .. 2*tries)]);
s1 := Array([seq(A[i]^2+A[tries+i]^2, i = 1 .. tries)]);
Mean(s1);
Variance(s1);
s2 := Array([seq(GenerateFloat()^2+GenerateFloat()^2, i = 1 .. tries)]);
Mean(s2);
Variance(s2);
output is:
0.6702112097021581
0.17845439723457215
0.664707674135025
0.35463131700965245
What's wrong with it? GenerateFloat() should be as uniform as possible.
Automatic simplification is turning your,
GenerateFloat()^2+GenerateFloat()^2
into,
2*GenerateFloat()^2
before GenerateFloat() is evaluated.
One simple change to get it to work as you expected would be separate them. Eg,
restart:
with(RandomTools[MersenneTwister]):
tries := 10^4:
s := 0:
for i to tries do
t1,t2 := GenerateFloat(),GenerateFloat();
if t1^2+t2^2 < 1 then s := s+1 end if;
end do:
evalf(4*s/tries);
Another way is to use a slightly different construction which doesn't automatically simplify. Consider, single right quotes (uneval quotes) don't stop automatic simplification (which is a definition of the term if you want).
'f()^2 + f()^2';
2
2 f()
But the following does not automatically simplify,
a:=1:
'f()^2 + a*f()^2';
2 2
f() + a f()
Therefore another easy workaround is,
restart:
with(RandomTools[MersenneTwister]):
tries := 10^4:
s := 0:
a := 1;
for i to tries do
if GenerateFloat()^2 + a*GenerateFloat()^2 < 1 then s := s+1 end if;
end do:
evalf(4*s/tries);
I know how to do basic exception handling. So i can raise a message on divide by zero using the 'try except' method.
What i would like to do is, find the variable that causes this error and then change its value on run time.
For Ex:
procedure Calculate();
var
a, b, c : Double;
begin
try
a := 4; //suppose i take this value from user and he enters 4
b := 0; //suppose i take this value from user and he enters 0
c := a/b;
ShowMessage(FloatToStr(c));
except
on E : EZeroDivide do
begin
ShowMessage('Exception message = '+E.Message);
//i am not sure how to identify that its variable 'b' that is causing the error and has to be changed by a default value
get(E....errorVaraiable);
E....errorVaraiable := 0.00001;
c := a/E....errorVariable;
ShowMessage(FloatToStr(c));
end;
end;
Please, can anyone help me with this?
Here's a modified version of your example that does what you want.
procedure Calculate();
var
a, b, c : Double;
begin
a := 4; //suppose i take this value from user and he enters 4
b := 0; //suppose i take this value from user and he enters 0
if IsZero(b) then
begin
ShowMessage('b cannot be 0')
end
else
begin
c := a/b;
ShowMessage(FloatToStr(c));
end;
end;