在 Octave/Matlab 中类型转换为 int

Question

I need to call the index of a matrix made using the linspace command, and based on some data taken from an oscilloscope. Because of this, the data inputed is a double. However, I can't really call:

Time[V0Found]

where V0Found is something like 5.2 however, taking index 5 is close enough, so I need to drop the decimal. I used this equation to drop the decimal:

V0FoundDec = V0Found - mod(V0Found,1)
Time[V0FoundDec]

However, even though that drops the decimal, octave still complains about it.

So, what can I do to typecast it to an int?

Answer 1

In MATLAB, it should be int8(x) or int16(x) or one of the other integer casts .

But I'm surprised you need to do that for an index. Try

myarray(floor(indexlist))

or

myarray(round(indexlist))

where myarray is your array and indexlist is your vector of noninteger indices.

---

example:

octave-3.2.3:8> v=rand(1,8)*10+1
v =

   3.1769   1.4397   8.7504   1.7424   6.9413   3.1663   8.4085   9.0179

octave-3.2.3:9> a = (1:1:20).^2
a =

 Columns 1 through 15:

     1     4     9    16    25    36    49    64    81   100   121   144   169   196   225

 Columns 16 through 20:

   256   289   324   361   400

octave-3.2.3:10> a(floor(v))
ans =

    9    1   64    1   36    9   64   81

Answer 2

You could use round , floor , ceil functions instead of your formula to do the rounding.

By the way, indexing is done using parenthesis instead of brackets so:

V0FoundDec = round(V0Found);
Time(V0FoundDec) % not Time[V0FoundDec]

In case that was your problem

Answer 3

In matlab, the right way to do this is to use the interp1 command to interpolate. The format of this command is

yout = interp1 (xdata, ydata, xin, ...) or yout = interp1 (ydata, xin, ...) where xdata is then assumed to be 1:length(ydata)

If you want to produce the result you would get from calling

V0FoundDec = Time(round(V0found))

you would say

V0FoundDec = interp1(Time, V0found, 'nearest')

but you can just as easily get linear interpolation (this is the default) with

V0FoundDec = interp1(Time, V0found)

or

V0FoundDec = interp1(Time,V0found,'linear')

and you can also extrapolate outside the limits (using 'extrap' or providing an extrap value), where

Time(round(V0found))

will crash if round(V0found) < 1 or > length(Time)

Answer 4

For those using Octave, the cast function does the job:

octave:1> cast(5.2,'int8')
ans = 5