fir1 — Design windowed-sinc FIR filters.
fir1(n, Wn) designs an order-n FIR filter using a Hamming-windowed sinc response. Scalar Wn creates a low-pass filter by default; a two-element Wn creates a band-pass filter by default. Add a filter type string for high-pass or stop-band designs.
Syntax
b = fir1(n, Wn)
b = fir1(n, Wn, ftype)
b = fir1(n, Wn, ftype, window, scaleopt)Inputs
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
n | SizeArg | Yes | — | Filter order. |
Wn | Any | Yes | — | Normalized cutoff frequency or two-element band. |
option | Any | Variadic | — | Filter type, window vector, or scale/noscale option. |
Returns
| Name | Type | Description |
|---|---|---|
b | NumericArray | FIR numerator coefficient row vector. |
Errors
| Identifier | When | Message |
|---|---|---|
RunMat:fir1:ArgCount | Fewer than two arguments are supplied. | fir1: expected fir1(n, Wn, ...) |
RunMat:fir1:InvalidOrder | The order is not a finite nonnegative integer scalar. | fir1: filter order must be a nonnegative integer |
RunMat:fir1:InvalidFrequency | Wn is not a valid normalized scalar or increasing two-element band. | fir1: invalid cutoff frequency |
RunMat:fir1:InvalidOption | A filter type, window vector, or scaling option is unsupported. | fir1: invalid option |
RunMat:fir1:Internal | Coefficient materialization fails internally. | fir1: internal error |
How fir1 works
- Returns a row vector with
n + 1coefficients. Wnuses MATLAB's normalized digital convention where1is Nyquist.- Supported filter types are
low,high,bandpass, andstop. - A custom window vector of length
n + 1may be supplied. - Filters are scaled by default; pass
noscaleto skip passband normalization.
Does RunMat run fir1 on the GPU?
Resident numeric arguments currently gather for host-side coefficient design.
The result is currently a host double row vector; documented GPU output residency is not yet restored.
Examples
Design a low-pass FIR filter
b = fir1(4, 0.5);
fprintf('%d %.4f\n', length(b), sum(b));Expected output:
5 1.0000Design coefficients for a FIR low-pass response plot
fs = 1000;
fc = 100;
N = 51;
wn = fc / (fs/2);
b = fir1(N-1, wn, 'low');
[H, w] = freqz(b, 1, 512, fs);
fprintf('%d %.1f %.1f\n', length(b), w(1), w(end));Expected output:
51 0.0 499.0Use a custom rectangular window without scaling
w = ones(1, 11);
b = fir1(10, 0.3, w, 'noscale');Using fir1 with coding agents
Open a RunMat example with live inputs, then ask the agent to explain how fir1 changes the result.
Run a small fir1 example, explain the result, then change one input and compare the output.
FAQ
What window does fir1 use by default?⌄
RunMat uses a symmetric Hamming window, matching MATLAB's default FIR design workflow.
Can the coefficients be used with filtfilt?⌄
Yes. Use filtfilt(b, 1, x) for zero-phase FIR filtering.
Does fir1 run on the GPU?⌄
The current implementation gathers resident numeric arguments and returns host double coefficients. Returning the documented resident GPU result remains a tracked compatibility gap.
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blackman · butter · buttord · cheb2ord · conv · conv2 · deconv · downsample · envelope · filter · filtfilt · freqz · gauspuls · hamming · hann · hilbert · periodogram · pulstran · pwelch · rectpuls · resample · sawtooth · sinc · spectrogram · square · tripuls · unwrap · upsample · zplane
Elementwise
abs · angle · bsxfun · complex · conj · double · erf · erfcinv · exp · expm1 · factorial · flintmax · gamma · gammaln · heaviside · hypot · idivide · imag · intmax · intmin · ldivide · log · log10 · log1p · log2 · minus · nextpow2 · plus · pow2 · power · rdivide · real · realmax · realmin · realsqrt · rescale · sign · single · sqrt · swapbytes · times · typecast · uint16 · uint32 · uint8
Trigonometry
acos · acosh · asin · asinh · atan · atan2 · atanh · cos · cosd · cosh · cospi · deg2rad · pol2cart · rad2deg · sin · sind · sinh · sinpi · tan · tand · tanh
Reduction
all · any · bounds · cummax · cummin · cumprod · cumsum · cumtrapz · diff · gradient · max · maxk · mean · median · min · mink · movmax · movmean · movmedian · movmin · movprod · movstd · movsum · movvar · nnz · prod · rms · std · sum · trapz · var
Structure
bandwidth · isdiag · ishermitian · issymmetric · istril · istriu · symrcm
Optim
coneprog · fminbnd · fminunc · fsolve · fzero · integral · linprog · lsqcurvefit · lsqnonlin · optimoptions · optimset · quad · secondordercone
Ops
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Open-source implementation
Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how fir1 is executed, line by line, in Rust.
- View the source for fir1 in Rust on GitHub
- Learn how the RunMat runtime works
- Found a bug? Open an issue with a minimal reproduction.
About RunMat
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