Fix latex() and unicode(), and seek the advice of Derivative by Xingye-Dujing · Pull Request #2132 · symengine/symengine

Xingye-Dujing · 2026-01-27T04:26:35Z

#2131
In the function UnicodePrinter::bvisit(const Add &x), when x.get_coef() is zero and the first term’s multiplier is -1, the expression is printed as the negative of the original via unicode(*expr).

Xingye-Dujing · 2026-01-27T10:12:16Z

Description

I discovered a problem with the latex() function. When we compile and run in the Debug environment, the behavior of something like Derivative::create(mul(sin(x), cos(x)), {x}); will be blocked by is_canonical(). However, if we use the Release version, the above code will run normally. At this point, calling latex(* Derivative()) will cause an issue.
Here is an example to illustrate:

diff = Derivative::create(add(sin(x), cos(x)), {x});
expr = add(diff, x);
std::cout << latex(*expr) << '\n';

The result is

x + \frac{d}{d x} \sin{\left(x\right)} + \cos{\left(x\right)}

It is lacking (), which has led to the incorrect display of the differentially expressed formula.
The correct result should be

x + \frac{d}{d x} (\sin{\left(x\right)} + \cos{\left(x\right)})

Fix

This issue was triggered by the function void LatexPrinter::bvisit(const Derivative &x).
Just remove the ending part.

s << "} " << apply(x.get_arg());
str_ = s.str();

Change to

const RCP<const Basic> arg = x.get_arg();
std::string arg_str = apply(arg);
if (is_a<Add>(*arg) || is_a<Mul>(*arg)) {
    arg_str = "\\left(" + arg_str + "\\right)";
}
s << "} " << arg_str;
str_ = s.str();

End

Since this behavior falls under the category of improper usage by the users, I would like to first inquire whether it is necessary to take this into consideration. If deemed necessary, I will submit the amendments.

Xingye-Dujing · 2026-01-27T10:34:24Z

Description

I want to enhance the functionality of the class Derivative.

Remove the is_canonical() restriction. We can now use the Derivative object more freely.
Add a doit() method, similar to how SymPy operates.
Expand the unicode() function to enable a more visually appealing display of the Derivative object.

Proposed implementation

To maintain compatibility, we directly create a new constructor.

Derivative::Derivative(const RCP<const Basic>& arg, const multiset_basic& x, const bool&)
    : arg_{ arg }, x_{ x }
{
    SYMENGINE_ASSIGN_TYPEID()
}

This way, even in the Debug environment, the check of is_canonical() can be skipped.

Derivative add new methods

RCP<const Basic> Derivative::doit() const
{
    return this->arg_->diff(rcp_static_cast<const Symbol>(*x_.begin()));
}

UnicodePrinter add new methods

void UnicodePrinter::bvisit(const Derivative& x)
{
	const auto& symbols = x.get_symbols();
	StringBox Box;

	if (symbols.size() == 1) {
		if (free_symbols(*x.get_arg()).size() == 1) {
			StringBox box("d");
			StringBox div_d("d" + str(*(*(symbols.begin()))), 2);
			box.add_below_unicode_line(div_d);
			Box.add_right(box);
		}
		else {
			StringBox box(U8("\u2202"), 1);
			StringBox div_d(U8("\u2202") + str(*(*(symbols.begin()))), 2);
			box.add_below_unicode_line(div_d);
			Box.add_right(box);
		}
	}
	else
	{
		StringBox div_d, box(U8("\u2202") + std::to_string(symbols.size()), 2);
		unsigned count = 1;
		auto it = symbols.begin();
		RCP<const Basic> prev = *it;
		++it;
		for (; it != symbols.end(); ++it) {
			if (neq(*prev, **it)) {
				if (count == 1)
				{
					div_d.add_right(StringBox(U8("\u2202") + str(*prev), 2));
				}
				else
				{
					div_d.add_right(StringBox(U8("\u2202") + str(*prev) + std::to_string(count), 3));
				}
				count = 1;
			}
			else {
				count++;
			}
			prev = *it;
		}
		if (count == 1) {
			div_d.add_right(StringBox(U8("\u2202") + str(*prev), 2));
		}
		else {
			div_d.add_right(StringBox(U8("\u2202") + str(*prev) + std::to_string(count), 3));
		}

		box.add_below_unicode_line(div_d);
		Box.add_right(box);
	}

	const RCP<const Basic> arg = x.get_arg();
	StringBox arg_box = apply(arg);
	StringBox pad_arg_box(" ");
	if (is_a<Add>(*arg) || is_a<Mul>(*arg)) {
		arg_box.enclose_parens(true);
		pad_arg_box = arg_box;
	}
	else
	{
		pad_arg_box.add_right(arg_box);
	}

	Box.add_right(pad_arg_box);
	box_ = Box;
}

Note: For the sake of aesthetic presentation, I did not use add_power(), but instead used add_right(). Here, the introduction of add_power() is unnecessary and would be unattractive.

Improve UnicodePrinter::_print_pow() for Derivative

void StringBox::enclose_parens(const bool& big)
{
	add_left_parens(big);
	add_right_parens();
}

void StringBox::add_left_parens(const bool& big)
{
	if (lines_.size() == 1)
	{
		if (big)
		{
			const std::string pad(width_, ' ');
			lines_.insert(lines_.begin(), pad);
			lines_.insert(lines_.end(), pad);
			lines_[0].insert(0, U8("\u239B "));
			lines_.back().insert(0, U8("\u239D "));
			for (unsigned i = 1; i < lines_.size() - 1; i++) {
				lines_[i].insert(0, U8("\u239C "));
			}
			width_ += 2;
		}
		else {
			width_ += 1;
			lines_[0].insert(0, "(");
		}
	}
	else {
		lines_[0].insert(0, U8("\u239B "));
		lines_.back().insert(0, U8("\u239D "));
		for (unsigned i = 1; i < lines_.size() - 1; i++) {
			lines_[i].insert(0, U8("\u239C "));
		}
		width_ += 2;
	}
}

void UnicodePrinter::_print_pow(const RCP<const Basic>& a,
	const RCP<const Basic>& b)
{
	if (eq(*b, *rational(1, 2))) {
		StringBox box = apply(a);
		box.enclose_sqrt();
		box_ = box;
	}
	else {
		StringBox base;
		if (is_a<Derivative>(*a))
		{
			base = apply(a);
			base.enclose_parens(true);
		}
		else
		{
			base = parenthesizeLE(a, PrecedenceEnum::Pow);
		}
		StringBox exp = parenthesizeLE(b, PrecedenceEnum::Pow);
		base.add_power(exp);
		box_ = base;
	}
}

fix the problem of latex(*Derivative).

End

Do you think this expansion is necessary? If you think it is, I will submit my implementation plan.

Xingye-Dujing · 2026-01-27T14:12:38Z

Description

I have discovered another issue with the unicode() function. It is void StringBox::add_power(StringBox& other) Caused. When exp is greater than one line, it will completely reversly output it.

Fix

All need to do is reverse other.lines_.

void StringBox::add_power(StringBox& other)
{
	for (std::string& line : lines_) {
		line.append(std::string(other.width_, ' '));
	}
	std::reverse(other.lines_.begin(), other.lines_.end());
	for (std::string& line : other.lines_) {
		lines_.insert(lines_.begin(), std::string(width_, ' ') + line);
	}
	width_ += other.width_;
}

Xingye-Dujing · 2026-01-28T13:07:56Z

Now I have fixed the issues I discovered in latex() and unicode(), and there is still the expansion of Derivative functions awaiting for feedback.

…ul sign

Xingye-Dujing · 2026-02-01T16:52:06Z

Description

Sometimes, the unicode() function mistakenly add two '-'.

unicode:2 - -3.y
str: 2 - 3*y

Solution

Use abs to handle the coef (add the '-' separately at the end).

else {
    t = parenthesizeLT(abs(p.second), PrecedenceEnum::Mul);                   # abs(p.second)
    auto op = print_mul();
    t.add_right(op);
    auto rhs = parenthesizeLT(p.first, PrecedenceEnum::Mul);
    t.add_right(rhs);
}

Xingye-Dujing · 2026-02-01T16:57:58Z

Description

When the numerator is 1, the num will mistakenly add an extra multiplication sign.

Solution

Just delete box1.add_right(mulbox); (See the submitted code)

Xingye-Dujing · 2026-02-02T21:09:41Z

Description

Simplify the -1 of the num to - for output.

Solution

Just add a special case handling when the numerator is -1. (See the submitted code)

Co-authored-by: Isuru Fernando <isuruf@gmail.com>

Fix void UnicodePrinter::bvisit(const Add &x)

f8f39d3

Fix void LatexPrinter::bvisit(const Derivative &x)

9be6e7c

Xingye-Dujing changed the title ~~Fix void UnicodePrinter::bvisit(const Add &x)~~ Fix latex() and unicode() Jan 28, 2026

// Fix void StringBox::add_power(StringBox& other)

e70713e

Xingye-Dujing changed the title ~~Fix latex() and unicode()~~ Fix latex() and unicode(), and seek the advice of Derivative Jan 28, 2026

Xingye-Dujing added 3 commits February 2, 2026 00:11

Fix void UnicodePrinter::bvisit(const Add &x): double minus error

1cb6a47

Fix void UnicodePrinter::bvisit(const Mul &x): remove the redundant m…

c5ad800

…ul sign

Fix test case

7d74598

Simplify the -1 of the num to -

5a6f706

isuruf reviewed Feb 12, 2026

View reviewed changes

Comment thread symengine/printers/latex.cpp Outdated

Xingye-Dujing and others added 2 commits February 13, 2026 21:42

Update symengine/printers/latex.cpp

6f13a9e

Co-authored-by: Isuru Fernando <isuruf@gmail.com>

Merge branch 'symengine:master' into fix

d9e7457

isuruf requested a review from rikardn June 1, 2026 15:52

Merge branch 'master' into fix

095b569

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Fix latex() and unicode(), and seek the advice of Derivative - #2132

Fix latex() and unicode(), and seek the advice of Derivative#2132
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