Selector — Control Systems/Signal Routing

Selector

Control Systems / Signal Routing

Selects entries out of a vector signal by position: y = u(idx). The list of positions is fixed by the dialog and does not change while the model runs, so the output's length is known before the run starts. The output keeps the input's orientation – a column in gives a column out, a row gives a row.

Ports

• Input – the signal u to select from. It must be a vector: [m,1] or [1,n]. A [1,1] signal is a vector of one entry; a signal with both dimensions above 1 is reported rather than flattened.
• Output – y, the selected entries in the order they are listed, in the input's orientation. Its length is the number of positions selected, which is generally NOT the input's length: [m,1] in gives [L,1] out and [1,n] gives [1,L].

Parameters

• Index Mode – what the FIRST entry of the input is called.
  • One-based – the first entry is 1. The default, as in Simulink.
  • Zero-based – the first entry is 0.
• Index Option – how the list of positions is given. This selects which list is built rather than retuning one, so each option is a separate code path.
  • Select all – every entry, in order. "Indices" and "Output Size" are not read.
  • Index vector (dialog) – the positions listed in "Indices", in the order given. Repeats are allowed; the default.
  • Starting index (dialog) – a contiguous run of "Output Size" entries beginning at the single position in "Indices".
• Indices – the positions, counted according to Index Mode. A row or column vector under Index vector (dialog) ([1 3] by default), and a single position under Starting index (dialog). Every position must lie inside the input; one that does not stops the run with a message naming it.
• Output Size – how many entries the contiguous run takes. Read only under Starting index (dialog); a positive whole number.
• Input Port Width – how many entries the incoming signal has. It must agree with the signal that actually arrives, and a disagreement stops the run. It is not redundant: Simulink's own dialog carries this field and validates the index list against it, so the value has to cross the bridge for a generated script to run at all.
• Sampling Time (s) – zero or less inherits the solver's rate; a positive value runs the block at that period.

Code export

All ten targets: Python, MATLAB, Java, Rust, C, C++, VHDL, Verilog, SystemVerilog and PLC Structured Text. The whole index list is resolved at export time, so the generated body is a fixed set of copies with constant subscripts – no index arithmetic and no bounds test at run time, and nothing is exposed as a tunable parameter. Re-export after changing the selection. The three HDL targets are fully synthesizable: a gather with constant indices is wiring, so nothing is evaluated in real.

Simulink bridge

Import and export, mapped to simulink/Signal Routing/Selector. "Index Mode" to IndexMode and "Index Option" to IndexOptions, each one option for one option, so both round trips are lossless; "Input Port Width" to InputPortWidth, "Indices" to Indices and "Output Size" to OutputSizes as plain pass-through values. The width is written before the indices, deliberately: Simulink range-checks the index list against the declared width the moment it is set, and setting them the other way round is a hard error that aborts the whole generated script rather than a warning.

NumberOfDimensions is always written as 1 and RuntimeRangeChecks as off. This block selects along ONE dimension with indices that cannot move, so it has no second dimension to offer and nothing to range-check at run time – and pinning both means a Simulink model that uses a second dimension, or takes its indices from a port, is reported on import rather than quietly mapped onto a selection that would answer differently. "Sampling Time (s)" to SampleTime, as on every block.

Notes

• Algebraic, with no state: the output depends only on the current input.
• The output is a different SIZE from the input, which is the whole point of the block, and it is fixed for the run. A downstream block that requires its inputs to agree in size must be given signals that do.
• Repeats are allowed under Index vector (dialog): [2 2 1] is a legal selection and copies the second entry twice.
• No state space, deliberately. The gather is linear, but the block's output is a different size from its input, so it is not the SISO shape model reduction merges; carrying one would offer it for merges it cannot serve.
• To pick one entry with an index that ARRIVES ON A WIRE rather than sitting in the dialog, use Signal Routing / Multiport Switch with a single data input – that is what Simulink calls Index Vector.