regenerate kernel Horner coeffs: scaled to max val 1, and shave off s…

…ome degrees for upsampfac=1.25 (#499)

* gen_all_horner_cpp_header.m 1st try

* new ES kernel generation

* regen ES kernel with max size 1 not exp(beta)

* fix constexpr in matlab-gen ES kernel code

* done rescaling ES kernel to max value 1, regen all coeffs, fixes #454

* src/ker_horner_allw_loop_constexpr.c

* add 1 to degree for larger-w upsampfac=1.25 ker eval, recovers prior accuracy

* fix 1dtest issue re allowing ier=1 (warning only), #500

* more automated matlb kernel coeff generation

* automated and documented matlab kernel coefficient generation; tweaked the poly degrees for kernel, checked accuracy

* regen ker coeffs .h without nc200() etc func; use .size() instead, much neater

* reverted matlab before clang-format messed it up

* clang-formatted regen with assert logic fixed in .h horner stuff

CHANGELOG

@@ -1,8 +1,10 @@
 List of features / changes made / release notes, in reverse chronological order.
 If not stated, FINUFFT is assumed (cuFINUFFT <=1.3 is listed separately).
 
-V 2.3.0beta (6/21/24)
+V 2.3.0beta (7/21/24)
 
+* ES kernel rescaled to max value 1, reduced horner degrees for upsampfac=1.25
+  (fixes fp32 overflow issue #454).
 * Major acceleration of spread/interp kernels using XSIMD header-only lib,
   kernel evaluation, templating by ns with AVX-width-dependent decisions.
   Up to 80% faster, dep on compiler. (Marco Barbone with help from Libin Lu).

devel/README

@@ -0,0 +1,24 @@
+Developer and experimental codes for FINUFFT
+--------------------------------------------
+
+For generating kernel coefficient codes in ../src,
+the developer must run from MATLAB the following:
+
+gen_all_horner_C_code.m        : writes C-style Horner coeffs (pre-2024)
+  * a single call writes upsampfac=2 and 1.25
+  * calls gen_ker_horner_loop_C_code.m
+gen_all_horner_cpp_header.m    : writes C++ header Horner coeffs (July 2024 on)
+  * a single call writes upsampfac=2 and 1.25
+  * calls gen_ker_horner_loop_cpp_code.m
+
+Both of the gen_ker_* scripts call for the solve of the coeffs for each w:
+ker_ppval_coeff_mat.m
+  (which has the kernel definition in it, which must match spreadinterp.cpp)
+
+The universal location for kernel approximation (degree, ES beta setting) is:
+get_degree_and_beta.m
+Tweaks should be done here, and see instructions there for resulting acc test.
+Another code that has to match ../src/spreadinterp.cpp is:
+reverse_engineer_tol.m
+
+Barnett 7/22/24

devel/gen_all_horner_C_code.m

@@ -1,41 +1,39 @@
 % Script to make all C code for looped Horner eval of kernels of all widths.
 % writes to "ker" array, from a variable "z", and switches by width "w".
-% Resulting C code needs only placing in a function.
+% Now does both upsampfacs.
+% Resulting C code needs only including in a function.
 
 % Barnett 4/23/18; now calling Ludvig's loop version from 4/25/18.
 % version including low upsampfac, 6/17/18.
 % Ludvig put in w=4n padding, 1/31/20. Mystery about why d was bigger 2/6/20.
+% split out code for degree, beta, etc; loop upsampfacs Barnett 7/22/24.
 clear
 opts = struct();
 
-ws = 2:16;
-upsampfac = 2;       % sigma (upsampling): either 2 (default) or low (eg 5/4).
-opts.wpad = true;    % pad kernel eval to multiple of 4
+for upsampfac = [2.0, 1.25];   % sigma: either 2 (default) or low (eg 5/4)
+  fprintf('upsampfac = %g...\n',upsampfac)
+
+  ws = 2:16;
+  opts.wpad = true;    % pad kernel eval to multiple of 4
 
-if upsampfac==2, fid = fopen('../src/ker_horner_allw_loop.c','w');
-else, fid = fopen('../src/ker_lowupsampfac_horner_allw_loop.c','w');
-end
-fwrite(fid,sprintf('// Code generated by gen_all_horner_C_code.m in finufft/devel\n'));
-fwrite(fid,sprintf('// Authors: Alex Barnett & Ludvig af Klinteberg.\n// (C) The Simons Foundation, Inc.\n'));
-for j=1:numel(ws)
-  w = ws(j)
-  if upsampfac==2    % hardwire the betas for this default case
-    betaoverws = [2.20 2.26 2.38 2.30];   % matches setup_spreader
-    beta = betaoverws(min(4,w-1)) * w;    % uses last entry for w>=5
-    d = w + 2 + (w<=8);                   % between 2-3 more degree than w
-  else               % use formulae, must match params in setup_spreader...
-    gamma=0.97;                           % safety factor
-    betaoverws = gamma*pi*(1-1/(2*upsampfac));  % from cutoff freq formula
-    beta = betaoverws * w;
-    d = w + 1 + (w<=8);                   % less, since beta smaller, smoother
+  if upsampfac==2, fid = fopen('../src/ker_horner_allw_loop_constexpr.c','w');
+  else, fid = fopen('../src/ker_lowupsampfac_horner_allw_loop_constexpr.c','w');
   end
-  str = gen_ker_horner_loop_C_code(w,d,beta,opts);
-  if j==1                                % write switch statement
-    fwrite(fid,sprintf('  if (w==%d) {\n',w));
-  else
-    fwrite(fid,sprintf('  } else if (w==%d) {\n',w));
+  fwrite(fid,sprintf('// Code generated by gen_all_horner_C_code.m in finufft/devel\n'));
+  fwrite(fid,sprintf('// Authors: Alex Barnett & Ludvig af Klinteberg.\n// (C) The Simons Foundation, Inc.\n'));
+  for j=1:numel(ws)
+    w = ws(j);
+    [d,beta] = get_degree_and_beta(w,upsampfac);
+    fprintf('w=%d\td=%d\tbeta=%.3g\n',w,d,beta);
+    str = gen_ker_horner_loop_C_code(w,d,beta,opts);
+    if j==1                                % write switch statement
+      fwrite(fid,sprintf('  if constexpr(w==%d) {\n',w));
+    else
+      fwrite(fid,sprintf('  } else if constexpr(w==%d) {\n',w));
+    end
+    for i=1:numel(str); fwrite(fid,['    ',str{i}]); end
   end
-  for i=1:numel(str); fwrite(fid,['    ',str{i}]); end
+  fwrite(fid,sprintf('  } else\n    printf("width not implemented!\\n");\n'));
+  fclose(fid);
+
 end
-fwrite(fid,sprintf('  } else\n    printf("width not implemented!\\n");\n'));
-fclose(fid);

devel/gen_all_horner_cpp_header.m

@@ -0,0 +1,52 @@
+% Script to make C++ header for looped Horner eval of kernels of all widths,
+% for a particular opts.upsampfac (user to hand-choose below).
+% C++ version (now writes .h), uses constexpr to switch by width w.
+
+% Barnett 4/23/18; now calling Ludvig's loop version from 4/25/18.
+% version including low upsampfac, 6/17/18.
+% Ludvig put in w=4n padding, 1/31/20. Mystery about why d was bigger 2/6/20.
+% C++ header using constexpr of Barbone, replacing *_C_code.m. Barnett 7/16/24.
+% simplified to kill nc200() etc functions, Barbone + Barnett 7/22/24.
+clear
+%opts = struct();  % not needed yet
+
+for upsampfac = [2.0, 1.25]   % sigma: either 2 (default) or low (eg 5/4)
+  fprintf('upsampfac = %g...\n',upsampfac)
+
+  ws = 2:16;           % list of widths (the driver, rather than tols)
+                       % (must match MIN and MAX NSPREAD in source headers)
+  if upsampfac==2
+    fid = fopen('../src/ker_horner_allw_loop_constexpr.h','w');
+  elseif upsampfac==1.25
+    fid = fopen('../src/ker_lowupsampfac_horner_allw_loop_constexpr.h','w');
+  end
+  fwrite(fid,sprintf('// Header of static arrays of monomial coeffs of spreading kernel function in each\n'));
+  fwrite(fid,sprintf('// fine-grid interval. Generated by gen_all_horner_cpp_header.m in devel/\n'));
+  fwrite(fid,sprintf('// Authors: Alex Barnett, Ludvig af Klinteberg, Marco Barbone & Libin Lu.\n// (C) 2018--2024 The Simons Foundation, Inc.\n'));
+  fwrite(fid,sprintf('#include <array>\n\n'));
+
+  usf_tag = sprintf('%d',100*upsampfac);  % string, follow Barbone convention: 200 or 125
+  fwrite(fid,sprintf('template<class T, uint8_t w>\nconstexpr auto get_horner_coeffs_%s() noexcept {\n',usf_tag));
+
+  for j=1:numel(ws)
+    w = ws(j);
+    [d,beta] = get_degree_and_beta(w,upsampfac);
+    fprintf('w=%d\td=%d\tbeta=%.3g\n',w,d,beta);
+    str = gen_ker_horner_loop_cpp_code(w,d,beta);  % code strings for this w (nc hardcoded)
+
+    if j==1                                % write switch statement
+      fwrite(fid,sprintf('    if constexpr (w == %d) {\n',w));
+    else
+      fwrite(fid,sprintf('    } else if constexpr (w == %d) {\n',w));
+    end
+    for i=1:numel(str); fwrite(fid,['    ',str{i}]); end   % format 4 extra spaces
+  end
+
+  % handle bad w at compile time...
+  fwrite(fid,sprintf('    }\n'));
+  fwrite(fid,sprintf('    static_assert(w >= %d, "w must be >= %d");\n',ws(1),ws(1)));
+  fwrite(fid,sprintf('    static_assert(w <= %d, "w must be <= %d");\n',ws(end),ws(end)));
+  fwrite(fid,sprintf('  };\n'));    % close all brackets
+  fclose(fid);
+
+end

devel/gen_ker_horner_loop_C_code.m

@@ -5,11 +5,12 @@
 %
 % Inputs:
 %  w = integer kernel width in grid points, eg 10
-%  d = poly degree to keep, eg 13
-%  beta = kernel parameter, around 2.3*w
+%  d = 0 (auto), or poly degree to keep, eg 13. (passed to ker_ppval_coeff_mat)
+%  beta = kernel parameter, around 2.3*w (for upsampfac=2)
 %  opts - optional struct, with fields:
 %         wpad - if true, pad the number of kernel eval (segments) to w=4n
 %                for SIMD speed, esp. w/ GCC<=5.4
+%         cutoff - desired coeff cutoff for this kernel, needed when d=0
 %         [ideas: could use to switch to cosh kernel variant, etc..]
 %
 % Outputs:
@@ -23,18 +24,20 @@
 % (Horner can't be vectorized in the degree direction; Estrin was no faster.)
 
 % Ludvig af Klinteberg 4/25/18, based on Barnett 4/23/18. Ludvig wpad 1/31/20.
+% Barnett fixed bug where degree was d-1 not d throughout; auto-d opt, 7/22/24.
 if nargin==0, test_gen_ker_horner_loop_C_code; return; end
 if nargin<4, o=[]; end
 
 C = ker_ppval_coeff_mat(w,d,be,o);
-str = cell(d+1,1);
+if d==0, d = size(C,2)-1; end
+str = cell(d+2,1);
 if isfield(o,'wpad') && o.wpad
   width = 4*ceil(w/4);
   C = [C zeros(size(C,1),width-w)];    % pad coeffs w/ 0, up to multiple of 4
 else
   width = w;
 end
-for n=1:d                  % loop over poly coeff powers
+for n=1:d+1                 % loop over poly coeff powers
   s = sprintf('FLT c%d[] = {%.16E',n-1, C(n,1));
   for i=2:width            % loop over segments
     s = sprintf('%s, %.16E', s, C(n,i));      
@@ -43,21 +46,21 @@
 end
 
 s = sprintf('for (int i=0; i<%d; i++) ker[i] = ',width);
-for n=1:d-1
+for n=1:d
   s = [s sprintf('c%d[i] + z*(',n-1)];   % (n-1)th coeff for i'th segment
 end
-s = [s sprintf('c%d[i]',d-1)];
-for n=1:d-1, s = [s sprintf(')')]; end  % close all parens
+s = [s sprintf('c%d[i]',d)];
+for n=1:d, s = [s sprintf(')')]; end  % close all parens
 s = [s sprintf(';\n')];          % terminate the C line, CR
-str{d+1} = s;
+str{d+2} = s;
 
 %%%%%%%%
 function test_gen_ker_horner_loop_C_code  % writes C code to file, doesn't test
-w=13; d=16;           % pick a single kernel width and degree to write code for
+w=13; d=0; opts.cutoff = 1e-12;   % pick a width and cutoff for degree
+beta=2.3*w;        % implies upsampfac=2
 %w=7; d=11;
 %w=2; d=5;
-beta=2.3*w;
-str = gen_ker_horner_loop_C_code(w,d,beta);
+str = gen_ker_horner_loop_C_code(w,d,beta,opts);
 % str{:}
 fnam = sprintf('ker_horner_w%d.c',w);
 fid = fopen(fnam,'w');

devel/gen_ker_horner_loop_cpp_code.m

@@ -0,0 +1,70 @@
+function str = gen_ker_horner_loop_cpp_code(w,d,be,o)
+% GEN_KER_HORNER_LOOP_CPP_CODE  Write C++ for piecewise poly coeffs of kernel
+%
+% str = gen_ker_horner_loop_cpp_code(w,d,be,o)
+%
+% Inputs:
+%  w = integer kernel width in grid points, eg 10
+%  d = 0 for auto, else poly degree to keep, eg 13.  (will give # coeffs nc=d+1)
+%  beta = kernel parameter, around 2.3*w (upsampfac=2 only)
+%  opts - optional struct, with fields: [none for now].
+%
+% Outputs:
+%  str = cell array of C++ code strings to define (d+1)*w static coeffs array,
+%        as in each w-specific block in ../src/ker_horner_allw_loop_constexpr.h
+%
+% Also see: KER_PPVAL_COEFF_MAT, FIG_SPEED_KER_PPVAL (which tests acc too)
+%           GEN_KER_HORNER_CPP_HEADER
+%
+% Notes:
+%
+% It exploits that there are w calls to different poly's w/ *same* z arg, writing
+% this as a loop. This allows the kernel evals at one z to be a w*nc mat-vec.
+% The xsimd code which uses this (see spreadinterp.cpp) is now too elaborate to
+% explain here.
+%
+% Changes from gen_ker_horner_loop_C_code.m:
+% i) a simple C++ style 2D array is written, with the w-direction fast, poly coeff
+%    direction slow. (It used to be a list of 1D arrays plus Horner eval code.)
+% ii) coeffs are now ordered c_d,c_{d-1},...,c_0, where degree d=nc-1. (Used
+%    to be reversed.)
+%
+% Ideas: could try PSWF, cosh kernel ES variant, Reinecke tweaked-power ES
+%  variant, etc..
+
+% Ludvig af Klinteberg 4/25/18, based on Barnett 4/23/18. Ludvig wpad 1/31/20.
+% Barnett redo for Barbone templated arrays, no wpad, 7/16/24.
+% hardcoded outer nc array size, 7/22/24.
+
+if nargin==0, test_gen_ker_horner_loop_cpp_code; return; end
+if nargin<4, o=[]; end
+
+C = ker_ppval_coeff_mat(w,d,be,o);
+if d==0, d = size(C,2)-1; end
+nc = d+1;
+str = cell(nc+2,1);     % one coeff per line + one return and one close-paren line
+% code to open the templated array...   why two {{?  (some C++ ambiguity thing)
+str{1} = sprintf('  return std::array<std::array<T, w>, %d> {{\n', nc);
+for n=1:d+1                  % loop over poly coeff powers 0,1,..,d
+  % sprintf implicitly loops over fine-grid interpolation intervals 1:w...
+  coeffrow = sprintf('%.16E, ', C(n,:));
+  coeffrow = coeffrow(1:end-2);   % easy kill trailing comma (but allowed in C++)
+  str{d+3-n} = sprintf('      {%s},\n', coeffrow);   % leave outer trailing comma
+end
+str{nc+2} = sprintf('  }};\n');     % terminate the array (two braces)
+
+
+%%%%%%%%
+function test_gen_ker_horner_loop_cpp_code  % writes code to file, doesn't test
+w=13; d=w+1;           % pick a single kernel width and degree to write code for
+%w=7; d=11;
+%w=2; d=5;
+beta=2.3*w;    % upsampfac=2 only
+str = gen_ker_horner_loop_cpp_code(w,d,beta);
+% str{:}
+% check write and read to file...
+fnam = sprintf('ker_horner_w%d.cpp',w);
+fid = fopen(fnam,'w');
+for i=1:numel(str); fwrite(fid,str{i}); end
+fclose(fid);
+system(['more ' fnam])

devel/get_degree_and_beta.m

@@ -0,0 +1,41 @@
+function [d,beta] = get_degree_and_beta(w,upsampfac)
+% GET_DEGREE_AND_BETA  defines degree & beta from w & upsampfac
+%
+% [d,beta] = get_degree_and_beta(w,upsampfac)
+%
+% Universal definition for piecewise poly degree chosen for kernel
+% coeff generation by matlab, and the ES kernel beta parameter.
+% The map from tol to width w must match code in spreadinterp used to
+% choose w.
+%
+% Used by all other *.m codes for generating coeffs.
+%
+% To test: use KER_PPVAL_COEFF_MAT self-test
+%
+% To verify accuracy in practice, compile FINUFFT CPU then run
+% test/checkallaccs.sh and matlab/test/fig_accuracy.m
+%
+% Also see: REVERSE_ENGINEER_TOL, KER_PPVAL_COEFF_MAT
+
+% Barnett 7/22/24
+if upsampfac==0.0, upsampfac=2.0; end
+
+% if d set to 0 in following, means it gets auto-chosen...
+if upsampfac==2    % hardwire the betas for this default case
+  betaoverws = [2.20 2.26 2.38 2.30];   % must match setup_spreader
+  beta = betaoverws(min(4,w-1)) * w;    % uses last entry for w>=5
+  d = w + 1 + (w<=7) - (w==2);          % between 1-2 more degree than w. tweak
+elseif upsampfac==1.25  % use formulae, must match params in setup_spreader
+  gamma=0.97;                           % safety factor
+  betaoverws = gamma*pi*(1-1/(2*upsampfac));  % from cutoff freq formula
+  beta = betaoverws * w;
+  d = ceil(0.7*w+1.3);                  % less, since beta smaller. tweak
+  %d = 0;    % auto-choose override? No, too much jitter.
+end
+
+if d==0
+  tol = reverse_engineer_tol(w,upsampfac);
+  opts.cutoff = 0.5 * tol;    % fudge to get more poly-approx acc than tol
+  C = ker_ppval_coeff_mat(w,0,beta,opts);    % do solve merely to get d
+  d = size(C,1)-1;            % extract the auto-chosen d
+end