# Question about data types while creating blocks **URL:** \ **Category:** GNU Radio\ **Created:** [June 7, 2015, 9:04am UTC](https://www.ruby-forum.com/t/question-about-data-types-while-creating-blocks/242234 "2015-06-07T09:04:48Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [June 7, 2015, 9:04am UTC](https://www.ruby-forum.com/t/question-about-data-types-while-creating-blocks/242234/1 "2015-06-07T09:04:48Z")
Hello I’m trying to create a new block, which one of its output variables is string. I would like to know if that it’s possible or if i should convert it to a integer type. This output is a vector of size 8, each with three characters: v[1] = ‘222’ v[2] =‘223’ v[3] =‘232’ v[4] =‘233’ v[5] =‘333’ v[6] =‘322’ v[7] =‘323’ v[8] =‘332’ Also, i would like to know if i can transmit a double variable using the float type output. Thank you David. – View this message in context: [http://gnuradio.4.n7.nabble.com/question-about-data-types-while-creating-blocks-tp54075.html](http://gnuradio.4.n7.nabble.com/question-about-data-types-while-creating-blocks-tp54075.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![dcardona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/a698b9/32.png) [@dcardona](https://www.ruby-forum.com/u/dcardona)\ **Post date:** [June 7, 2015, 10:55am UTC](https://www.ruby-forum.com/t/question-about-data-types-while-creating-blocks/242234/2 "2015-06-07T10:55:13Z")
Hi David, > I’m trying to create a new block, which one of its output variables is > string. to be honest, processing strings does sound more like a message passing instead of a sample streaming kind of thing. But: > This output is a vector of size 8, each with three characters: > aha! Your strings aren’t the typical, variable length string! their > 8-tuples of 3-tuples of characters! > Basically, what you want seems to be a block that emits bytes, in > multiples of 24. > There’s two ways to achieve that: you can either define the io\_signature > of the block to let the item size be 1 byte (==sizeof(char), and then > use set\_output\_multiple(24), or you can have an io\_signature with an > item size of 24. But: I don’t think you’re giving us the whole picture, considering your example strings look all very specific. Maybe you want to explain a bit of what your block should do? > Also, i would like to know if i can transmit a double variable using the > float type output. > No. But you can still have a block outputting doubles! To explain: GNU Radio doesn’t actually care about what kind of data you put into your block’s output items. It just needs to know how big (in bytes) each item is. Floats are 4 byte long, doubles (well…) 8 bytes. Hence, a double is worth two float output items. You can just set the io\_signature of your block to sizeof(double) instead of (float) and GNU Radio will know that you want to exchange 8 byte items instead of4 byte items. However, there’s a reason you don’t see the double type being used very often in GNU Radio: SNR and dynamic range of the systems described are seldom limited by the single precision floating point’s numerical accuracy, and so almost all things just work on floats. Again: Maybe you have some insight in what you want to do, that you might want to share? Best regards, Marcus ---
**Author:** ![dcardona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/a698b9/32.png) [@dcardona](https://www.ruby-forum.com/u/dcardona)\ **Post date:** [June 7, 2015, 7:27pm UTC](https://www.ruby-forum.com/t/question-about-data-types-while-creating-blocks/242234/3 "2015-06-07T19:27:33Z")
Hi Marcus Thank you very much for your response. What i want to do in general, is a chaotic channel coding scheme (based in Lorenz system) that works in lte, and compare it with the channel coding schemes using conventionally (convolutional coding and turbocoding). That’s why i wrote you last week (May 31) doing some questions about the connection between a trellis encoder block (or pccc encoder block) with the ofdm mod and ofdm demod blocks and then with the viterbi combo block (or pccc decoder combo block). So, returning to the chaotic coding… The method i’m using requires first a learning process which consists in obtain 2^n sequences (in this case n= 3) each corresponding to 2^n values of the variable z crossing with 2 Poincare surfaces sections (also a vector) of the Lorenz system. Hence, each coordinate of the vector (v) is really a sequence of symbols. For example, z[1] corresponds to the v[1] sequence, z[2] with the v[2] sequence, and so on. I want to send this two vectors to a third block (explained below). On the other hand, i have to create a second block that makes a differential encoding; associating the bit 0 with a change of symbol in two consecutive crossing with the Poincare surfaces of section (i.e., ‘23’ or ‘32’) and the bit 1 with the repetition of the same symbol (i.e., ‘22’ or ‘33’). The second blocks output will entry in a third block, i should convert it to a string so i can compare it with the 2^n string sequences. This bock will send the z values, which are double (that’s why i was asking about the output type float) that are needed to represent the sequences required (based on the inputs from the second block). So, I was trying to create the first block, which makes the learning process. If n = 3, i guess i could simply define 8 vectors of size 3 for the symbol sequences and another vector of size 8 for the z values directly in the third block, this because there will be the same all the time. This way, i only have 2 blocks (the second and the third). But in the case n = 8), i would have to define more vectors manually (256 vectors each of size 8) and that is what i wanted to avoid. I want to probe with several values of n so i can compare the behavior. I have thought and i could do it till n = 6. it’s no to much to write 64 vectors of size 6 manually. If you see a easier way to do all this, i’m all ears. I don’t know if i explained myself but thank you very much anyway. Again i’m sorry for my English. David. – View this message in context: [http://gnuradio.4.n7.nabble.com/question-about-data-types-while-creating-blocks-tp54075p54078.html](http://gnuradio.4.n7.nabble.com/question-about-data-types-while-creating-blocks-tp54075p54078.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![dcardona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/a698b9/32.png) [@dcardona](https://www.ruby-forum.com/u/dcardona)\ **Post date:** [June 7, 2015, 7:49pm UTC](https://www.ruby-forum.com/t/question-about-data-types-while-creating-blocks/242234/4 "2015-06-07T19:49:45Z")
Hello again. Maybe i could use n as a parameter on the block and do what yo suggest; define in the io\_signature of the block to let the item size to be 1 byte and then maybe use the set\_output\_multiple(n\*2^n). Can i do something like this? Thank you. David – View this message in context: [http://gnuradio.4.n7.nabble.com/question-about-data-types-while-creating-blocks-tp54075p54079.html](http://gnuradio.4.n7.nabble.com/question-about-data-types-while-creating-blocks-tp54075p54079.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![dcardona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/a698b9/32.png) [@dcardona](https://www.ruby-forum.com/u/dcardona)\ **Post date:** [June 7, 2015, 8:28pm UTC](https://www.ruby-forum.com/t/question-about-data-types-while-creating-blocks/242234/5 "2015-06-07T20:28:53Z")
Hi David, yes, that’s absolutely possible. Just use n as a parameter of the constructor 🙂 Best regards, Marcus ---
**Author:** ![dcardona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/a698b9/32.png) [@dcardona](https://www.ruby-forum.com/u/dcardona)\ **Post date:** [June 7, 2015, 8:52pm UTC](https://www.ruby-forum.com/t/question-about-data-types-while-creating-blocks/242234/6 "2015-06-07T20:52:15Z")
Thank you very much Marcus. And to save the vectors in the third block, should i use the set\_history(n\*2^n)? how do i set the input i want to save? because i have 2 inputs – View this message in context: [http://gnuradio.4.n7.nabble.com/question-about-data-types-while-creating-blocks-tp54075p54081.html](http://gnuradio.4.n7.nabble.com/question-about-data-types-while-creating-blocks-tp54075p54081.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![dcardona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/a698b9/32.png) [@dcardona](https://www.ruby-forum.com/u/dcardona)\ **Post date:** [June 7, 2015, 9:17pm UTC](https://www.ruby-forum.com/t/question-about-data-types-while-creating-blocks/242234/7 "2015-06-07T21:17:23Z")
That sounds great, I will do that. Thank you very much Marcus, You really helped me. – View this message in context: [http://gnuradio.4.n7.nabble.com/question-about-data-types-while-creating-blocks-tp54075p54083.html](http://gnuradio.4.n7.nabble.com/question-about-data-types-while-creating-blocks-tp54075p54083.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![dcardona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/a698b9/32.png) [@dcardona](https://www.ruby-forum.com/u/dcardona)\ **Post date:** [June 7, 2015, 10:58pm UTC](https://www.ruby-forum.com/t/question-about-data-types-while-creating-blocks/242234/8 "2015-06-07T22:58:27Z")
On Sun, Jun 7, 2015 at 3:02 PM, Marcus Müller [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > [1] you need to have a vector of history lengths instead of a single > integer; maybe Tom has some input on that. I think a change as invasive as this needs someone to identify a serious need for it that’s beyond one use-case that can be solved in other ways. Tom ---
**Author:** ![dcardona](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/a698b9/32.png) [@dcardona](https://www.ruby-forum.com/u/dcardona)\ **Post date:** [June 7, 2015, 9:03pm UTC](https://www.ruby-forum.com/t/question-about-data-types-while-creating-blocks/242234/9 "2015-06-07T21:03:22Z")
you’re right, set\_history works on all inputs simultaneously. That’s an architectural constraint; I don’t think it would be /impossible/ to fix that, i.e. to make GNU Radio have different history per input buffer, but it’s going to break API and therefore it’s not going to be easy finding a good solution [1]. But unless you want to do upstream development (which is always welcome, by the way!), I’d recommend that you “emulate” additional history by overriding your block’s forecast() method and telling GNU Radio that you need the additional number of items to produce a given amount of output; there’s no obligation to always consume all your input. I must admit that I can’t really follow your coding scheme; that has nothing to do with your English (which is very good), but with the fact that I haven’t ever heard anything about chaotic coding. At any rate, it might be helpful if you made a sketch of how your flow graph _should_ look like, and put short descriptions what each stream transports in there. Best regards, Marcus [1] you need to have a vector of history lengths instead of a single integer; maybe Tom has some input on that.